[Android Software Development] cabloomi:
So Languages in android are hidden because of your CSC, location, region, or carrier

but not all Firmwares. just most

for the sony and htc its the same guide but for samsung it diffrent. lets start off with sony and htc

Use a root explorer or a root level file manager or you can just use adb pull and push

and get this file

"system/customize/CID/default.xml"

move it to your computer and edit it using NOTEDPAD++

You will see something like this

<?xml version="1.0" encoding="utf-8"?>
<customization_form>
<category name="system">
<module name="locale">
<function>
<set name="single">
<item name="total_list">en_US;es_US;fr_US;</item>
<item type="boolean" name="en_US">yes</item>
<item type="boolean" name="es_US">yes</item>
<item type="boolean" name="fr_US">yes</item>
</set>

You wanna edit it so it would look like this

<?xml version="1.0" encoding="utf-8"?>
<customization_form>
<category name="system">
<module name="locale">
<function>
<set name="single">
<item name="total_list">ar_AR;ar_BH;ar_DZ;ar_JO;ar_KW;ar_LB;ar_LY;ar_MA;ar_OM;ar_QA;ar_TN;bg_BG;bg_BY;bg_CS;bg_CZ;bg_EE;bg_HR;bg_HU;bg_LT;bg_LV;bg_PL;bg_RO;bg_SI;bg_SK;bg_UA;cs_BG;cs_BY;cs_CS;cs_CZ;cs_EE;cs_HR;cs_HU;cs_LT;cs_LV;cs_PL;cs_RO;cs_SI;cs_SK;cs_UA;da_DK;da_FI;da_NO;da_SE;de_AO;de_AT;de_CH;de_DE;de_ES;de_FR;de_GB;de_IE;de_IT;de_KE;de_LU;de_MZ;de_NA;de_NG;de_NL;de_PT;de_ZA;el_GR;en_AE;en_AM;en_AO;en_AT;en_AU;en_AZ;en_BG;en_BH;en_BY;en_CH;en_CS;en_CZ;en_DE;en_DK;en_DZ;en_EE;en_EG;en_ES;en_FI;en_FR;en_GB;en_GE;en_GR;en_HR;en_HU;en_ID;en_IE;en_IQ;en_IT;en_JO;en_KE;en_KW;en_KZ;en_LB;en_LT;en_LU;en_LV;en_LY;en_MA;en_MZ;en_NA;en_NG;en_NL;en_NO;en_OM;en_PL;en_PT;en_QA;en_RO;en_RU;en_SA;en_SE;en_SG;en_SI;en_SK;en_TN;en_UA;en_US;en_ZA;es_ES;es_FR;es_GB;es_IE;es_IT;es_PT;es_US;fi_DK;fi_FI;fi_NO;fi_SE;fr_AE;fr_AO;fr_AT;fr_BH;fr_CH;fr_DE;fr_DZ;fr_EG;fr_ES;fr_FR;fr_GB;fr_IE;fr_IQ;fr_IT;fr_JO;fr_KE;fr_KW;fr_LB;fr_LU;fr_LY;fr_MA;fr_MZ;fr_NA;fr_NG;fr_NL;fr_OM;fr_PT;fr_QA;fr_SA;fr_TN;fr_US;fr_ZA;hi_HI;hr_BG;hr_BY;hr_CS;hr_CZ;hr_EE;hr_HR;hr_HU;hr_LT;hr_LV;hr_PL;hr_RO;hr_SI;hr_SK;hr_UA;hu_BG;hu_BY;hu_CS;hu_CZ;hu_EE;hu_HR;hu_HU;hu_LT;hu_LV;hu_PL;hu_RO;hu_SI;hu_SK;hu_UA;it_AT;it_CH;it_DE;it_FR;it_GB;it_IE;it_IT;iw_IW;ja_JP;ko_KR;nb_DK;nb_FI;nb_NO;nb_SE;nl_FR;nl_LU;nl_NL;nl_BE;pl_BG;pl_BY;pl_CS;pl_CZ;pl_EE;pl_GB;pl_HR;pl_HU;pl_IE;pl_LT;pl_LV;pl_PL;pl_RO;pl_SI;pl_SK;pl_UA;pt_AO;pt_ES;pt_FR;pt_KE;pt_MZ;pt_NA;pt_NG;pt_PT;pt_ZA;ro_BG;ro_BY;ro_CS;ro_CZ;ro_EE;ro_HR;ro_HU;ro_LT;ro_LV;ro_PL;ro_RO;ro_SI;ro_SK;ro_UA;ru_AM;ru_AZ;ru_BG;ru_BY;ru_CS;ru_CZ;ru_EE;ru_GE;ru_HR;ru_HU;ru_KZ;ru_LT;ru_LV;ru_PL;ru_RO;ru_RU;ru_SI;ru_SK;ru_UA;sk_BG;sk_BY;sk_CS;sk_CZ;sk_EE;sk_HR;sk_HU;sk_LT;sk_LV;sk_PL;sk_RO;sk_SI;sk_SK;sk_UA;sl_BG;sl_BY;sl_CS;sl_CZ;sl_EE;sl_HR;sl_HU;sl_LT;sl_LV;sl_PL;sl_RO;sl_SI;sl_SK;sl_UA;sr_BG;sr_BY;sr_CS;sr_CZ;sr_EE;sr_HR;sr_HU;sr_LT;sr_LV;sr_PL;sr_RO;sr_SI;sr_SK;sr_UA;sv_DK;sv_FI;sv_NO;sv_SE;th_TH;tr_AT;tr_CH;tr_DE;tr_TR;vi_VN;zh_CN;zh_HK;zh_TW;</item>
<item type="boolean" name="ar_AR">yes</item>
<item type="boolean" name="ar_BH">yes</item>
<item type="boolean" name="ar_DZ">yes</item>
<item type="boolean" name="ar_JO">yes</item>
<item type="boolean" name="ar_KW">yes</item>
<item type="boolean" name="ar_LB">yes</item>
<item type="boolean" name="ar_LY">yes</item>
<item type="boolean" name="ar_MA">yes</item>
<item type="boolean" name="ar_OM">yes</item>
<item type="boolean" name="ar_QA">yes</item>
<item type="boolean" name="ar_TN">yes</item>
<item type="boolean" name="bg_BG">yes</item>
<item type="boolean" name="bg_BY">yes</item>
<item type="boolean" name="bg_CS">yes</item>
<item type="boolean" name="bg_CZ">yes</item>
<item type="boolean" name="bg_EE">yes</item>
<item type="boolean" name="bg_HR">yes</item>
<item type="boolean" name="bg_HU">yes</item>
<item type="boolean" name="bg_LT">yes</item>
<item type="boolean" name="bg_LV">yes</item>
<item type="boolean" name="bg_PL">yes</item>
<item type="boolean" name="bg_RO">yes</item>
<item type="boolean" name="bg_SI">yes</item>
<item type="boolean" name="bg_SK">yes</item>
<item type="boolean" name="bg_UA">yes</item>
<item type="boolean" name="cs_BG">yes</item>
<item type="boolean" name="cs_BY">yes</item>
<item type="boolean" name="cs_CS">yes</item>
<item type="boolean" name="cs_CZ">yes</item>
<item type="boolean" name="cs_EE">yes</item>
<item type="boolean" name="cs_HR">yes</item>
<item type="boolean" name="cs_HU">yes</item>
<item type="boolean" name="cs_LT">yes</item>
<item type="boolean" name="cs_LV">yes</item>
<item type="boolean" name="cs_PL">yes</item>
<item type="boolean" name="cs_RO">yes</item>
<item type="boolean" name="cs_SI">yes</item>
<item type="boolean" name="cs_SK">yes</item>
<item type="boolean" name="cs_UA">yes</item>
<item type="boolean" name="da_DK">yes</item>
<item type="boolean" name="da_FI">yes</item>
<item type="boolean" name="da_NO">yes</item>
<item type="boolean" name="da_SE">yes</item>
<item type="boolean" name="de_AO">yes</item>
<item type="boolean" name="de_AT">yes</item>
<item type="boolean" name="de_CH">yes</item>
<item type="boolean" name="de_DE">yes</item>
<item type="boolean" name="de_ES">yes</item>
<item type="boolean" name="de_FR">yes</item>
<item type="boolean" name="de_GB">yes</item>
<item type="boolean" name="de_IE">yes</item>
<item type="boolean" name="de_IT">yes</item>
<item type="boolean" name="de_KE">yes</item>
<item type="boolean" name="de_LU">yes</item>
<item type="boolean" name="de_MZ">yes</item>
<item type="boolean" name="de_NA">yes</item>
<item type="boolean" name="de_NG">yes</item>
<item type="boolean" name="de_NL">yes</item>
<item type="boolean" name="de_PT">yes</item>
<item type="boolean" name="de_ZA">yes</item>
<item type="boolean" name="el_GR">yes</item>
<item type="boolean" name="en_AE">yes</item>
<item type="boolean" name="en_AM">yes</item>
<item type="boolean" name="en_AO">yes</item>
<item type="boolean" name="en_AT">yes</item>
<item type="boolean" name="en_AU">yes</item>
<item type="boolean" name="en_AZ">yes</item>
<item type="boolean" name="en_BG">yes</item>
<item type="boolean" name="en_BH">yes</item>
<item type="boolean" name="en_BY">yes</item>
<item type="boolean" name="en_CH">yes</item>
<item type="boolean" name="en_CS">yes</item>
<item type="boolean" name="en_CZ">yes</item>
<item type="boolean" name="en_DE">yes</item>
<item type="boolean" name="en_DK">yes</item>
<item type="boolean" name="en_DZ">yes</item>
<item type="boolean" name="en_EE">yes</item>
<item type="boolean" name="en_EG">yes</item>
<item type="boolean" name="en_ES">yes</item>
<item type="boolean" name="en_FI">yes</item>
<item type="boolean" name="en_FR">yes</item>
<item type="boolean" name="en_GB">yes</item>
<item type="boolean" name="en_GE">yes</item>
<item type="boolean" name="en_GR">yes</item>
<item type="boolean" name="en_HR">yes</item>
<item type="boolean" name="en_HU">yes</item>
<item type="boolean" name="en_ID">yes</item>
<item type="boolean" name="en_IE">yes</item>
<item type="boolean" name="en_IQ">yes</item>
<item type="boolean" name="en_IT">yes</item>
<item type="boolean" name="en_JO">yes</item>
<item type="boolean" name="en_KE">yes</item>
<item type="boolean" name="en_KW">yes</item>
<item type="boolean" name="en_KZ">yes</item>
<item type="boolean" name="en_LB">yes</item>
<item type="boolean" name="en_LT">yes</item>
<item type="boolean" name="en_LU">yes</item>
<item type="boolean" name="en_LV">yes</item>
<item type="boolean" name="en_LY">yes</item>
<item type="boolean" name="en_MA">yes</item>
<item type="boolean" name="en_MZ">yes</item>
<item type="boolean" name="en_NA">yes</item>
<item type="boolean" name="en_NG">yes</item>
<item type="boolean" name="en_NL">yes</item>
<item type="boolean" name="en_NO">yes</item>
<item type="boolean" name="en_OM">yes</item>
<item type="boolean" name="en_PL">yes</item>
<item type="boolean" name="en_PT">yes</item>
<item type="boolean" name="en_QA">yes</item>
<item type="boolean" name="en_RO">yes</item>
<item type="boolean" name="en_RU">yes</item>
<item type="boolean" name="en_SA">yes</item>
<item type="boolean" name="en_SE">yes</item>
<item type="boolean" name="en_SG">yes</item>
<item type="boolean" name="en_SI">yes</item>
<item type="boolean" name="en_SK">yes</item>
<item type="boolean" name="en_TN">yes</item>
<item type="boolean" name="en_UA">yes</item>
<item type="boolean" name="en_US">yes</item>
<item type="boolean" name="en_ZA">yes</item>
<item type="boolean" name="es_ES">yes</item>
<item type="boolean" name="es_FR">yes</item>
<item type="boolean" name="es_GB">yes</item>
<item type="boolean" name="es_IE">yes</item>
<item type="boolean" name="es_IT">yes</item>
<item type="boolean" name="es_PT">yes</item>
<item type="boolean" name="es_US">yes</item>
<item type="boolean" name="fi_DK">yes</item>
<item type="boolean" name="fi_FI">yes</item>
<item type="boolean" name="fi_NO">yes</item>
<item type="boolean" name="fi_SE">yes</item>
<item type="boolean" name="fr_AE">yes</item>
<item type="boolean" name="fr_AO">yes</item>
<item type="boolean" name="fr_AT">yes</item>
<item type="boolean" name="fr_BH">yes</item>
<item type="boolean" name="fr_CH">yes</item>
<item type="boolean" name="fr_DE">yes</item>
<item type="boolean" name="fr_DZ">yes</item>
<item type="boolean" name="fr_EG">yes</item>
<item type="boolean" name="fr_ES">yes</item>
<item type="boolean" name="fr_FR">yes</item>
<item type="boolean" name="fr_GB">yes</item>
<item type="boolean" name="fr_IE">yes</item>
<item type="boolean" name="fr_IQ">yes</item>
<item type="boolean" name="fr_IT">yes</item>
<item type="boolean" name="fr_JO">yes</item>
<item type="boolean" name="fr_KE">yes</item>
<item type="boolean" name="fr_KW">yes</item>
<item type="boolean" name="fr_LB">yes</item>
<item type="boolean" name="fr_LU">yes</item>
<item type="boolean" name="fr_LY">yes</item>
<item type="boolean" name="fr_MA">yes</item>
<item type="boolean" name="fr_MZ">yes</item>
<item type="boolean" name="fr_NA">yes</item>
<item type="boolean" name="fr_NG">yes</item>
<item type="boolean" name="fr_NL">yes</item>
<item type="boolean" name="fr_OM">yes</item>
<item type="boolean" name="fr_PT">yes</item>
<item type="boolean" name="fr_QA">yes</item>
<item type="boolean" name="fr_SA">yes</item>
<item type="boolean" name="fr_TN">yes</item>
<item type="boolean" name="fr_US">yes</item>
<item type="boolean" name="fr_ZA">yes</item>
<item type="boolean" name="hi_HI">yes</item>
<item type="boolean" name="hr_BG">yes</item>
<item type="boolean" name="hr_BY">yes</item>
<item type="boolean" name="hr_CS">yes</item>
<item type="boolean" name="hr_CZ">yes</item>
<item type="boolean" name="hr_EE">yes</item>
<item type="boolean" name="hr_HR">yes</item>
<item type="boolean" name="hr_HU">yes</item>
<item type="boolean" name="hr_LT">yes</item>
<item type="boolean" name="hr_LV">yes</item>
<item type="boolean" name="hr_PL">yes</item>
<item type="boolean" name="hr_RO">yes</item>
<item type="boolean" name="hr_SI">yes</item>
<item type="boolean" name="hr_SK">yes</item>
<item type="boolean" name="hr_UA">yes</item>
<item type="boolean" name="hu_BG">yes</item>
<item type="boolean" name="hu_BY">yes</item>
<item type="boolean" name="hu_CS">yes</item>
<item type="boolean" name="hu_CZ">yes</item>
<item type="boolean" name="hu_EE">yes</item>
<item type="boolean" name="hu_HR">yes</item>
<item type="boolean" name="hu_HU">yes</item>
<item type="boolean" name="hu_LT">yes</item>
<item type="boolean" name="hu_LV">yes</item>
<item type="boolean" name="hu_PL">yes</item>
<item type="boolean" name="hu_RO">yes</item>
<item type="boolean" name="hu_SI">yes</item>
<item type="boolean" name="hu_SK">yes</item>
<item type="boolean" name="hu_UA">yes</item>
<item type="boolean" name="it_AT">yes</item>
<item type="boolean" name="it_CH">yes</item>
<item type="boolean" name="it_DE">yes</item>
<item type="boolean" name="it_FR">yes</item>
<item type="boolean" name="it_GB">yes</item>
<item type="boolean" name="it_IE">yes</item>
<item type="boolean" name="it_IT">yes</item>
<item type="boolean" name="iw_IW">yes</item>
<item type="boolean" name="ja_JP">yes</item>
<item type="boolean" name="ko_KR">yes</item>
<item type="boolean" name="nb_DK">yes</item>
<item type="boolean" name="nb_FI">yes</item>
<item type="boolean" name="nb_NO">yes</item>
<item type="boolean" name="nb_SE">yes</item>
<item type="boolean" name="nl_FR">yes</item>
<item type="boolean" name="nl_LU">yes</item>
<item type="boolean" name="nl_NL">yes</item>
<item type="boolean" name="nl_BE">yes</item>
<item type="boolean" name="pl_BG">yes</item>
<item type="boolean" name="pl_BY">yes</item>
<item type="boolean" name="pl_CS">yes</item>
<item type="boolean" name="pl_CZ">yes</item>
<item type="boolean" name="pl_EE">yes</item>
<item type="boolean" name="pl_GB">yes</item>
<item type="boolean" name="pl_HR">yes</item>
<item type="boolean" name="pl_HU">yes</item>
<item type="boolean" name="pl_IE">yes</item>
<item type="boolean" name="pl_LT">yes</item>
<item type="boolean" name="pl_LV">yes</item>
<item type="boolean" name="pl_PL">yes</item>
<item type="boolean" name="pl_RO">yes</item>
<item type="boolean" name="pl_SI">yes</item>
<item type="boolean" name="pl_SK">yes</item>
<item type="boolean" name="pl_UA">yes</item>
<item type="boolean" name="pt_AO">yes</item>
<item type="boolean" name="pt_ES">yes</item>
<item type="boolean" name="pt_FR">yes</item>
<item type="boolean" name="pt_KE">yes</item>
<item type="boolean" name="pt_MZ">yes</item>
<item type="boolean" name="pt_NA">yes</item>
<item type="boolean" name="pt_NG">yes</item>
<item type="boolean" name="pt_PT">yes</item>
<item type="boolean" name="pt_ZA">yes</item>
<item type="boolean" name="ro_BG">yes</item>
<item type="boolean" name="ro_BY">yes</item>
<item type="boolean" name="ro_CS">yes</item>
<item type="boolean" name="ro_CZ">yes</item>
<item type="boolean" name="ro_EE">yes</item>
<item type="boolean" name="ro_HR">yes</item>
<item type="boolean" name="ro_HU">yes</item>
<item type="boolean" name="ro_LT">yes</item>
<item type="boolean" name="ro_LV">yes</item>
<item type="boolean" name="ro_PL">yes</item>
<item type="boolean" name="ro_RO">yes</item>
<item type="boolean" name="ro_SI">yes</item>
<item type="boolean" name="ro_SK">yes</item>
<item type="boolean" name="ro_UA">yes</item>
<item type="boolean" name="ru_AM">yes</item>
<item type="boolean" name="ru_AZ">yes</item>
<item type="boolean" name="ru_BG">yes</item>
<item type="boolean" name="ru_BY">yes</item>
<item type="boolean" name="ru_CS">yes</item>
<item type="boolean" name="ru_CZ">yes</item>
<item type="boolean" name="ru_EE">yes</item>
<item type="boolean" name="ru_GE">yes</item>
<item type="boolean" name="ru_HR">yes</item>
<item type="boolean" name="ru_HU">yes</item>
<item type="boolean" name="ru_KZ">yes</item>
<item type="boolean" name="ru_LT">yes</item>
<item type="boolean" name="ru_LV">yes</item>
<item type="boolean" name="ru_PL">yes</item>
<item type="boolean" name="ru_RO">yes</item>
<item type="boolean" name="ru_RU">yes</item>
<item type="boolean" name="ru_SI">yes</item>
<item type="boolean" name="ru_SK">yes</item>
<item type="boolean" name="ru_UA">yes</item>
<item type="boolean" name="sk_BG">yes</item>
<item type="boolean" name="sk_BY">yes</item>
<item type="boolean" name="sk_CS">yes</item>
<item type="boolean" name="sk_CZ">yes</item>
<item type="boolean" name="sk_EE">yes</item>
<item type="boolean" name="sk_HR">yes</item>
<item type="boolean" name="sk_HU">yes</item>
<item type="boolean" name="sk_LT">yes</item>
<item type="boolean" name="sk_LV">yes</item>
<item type="boolean" name="sk_PL">yes</item>
<item type="boolean" name="sk_RO">yes</item>
<item type="boolean" name="sk_SI">yes</item>
<item type="boolean" name="sk_SK">yes</item>
<item type="boolean" name="sk_UA">yes</item>
<item type="boolean" name="sl_BG">yes</item>
<item type="boolean" name="sl_BY">yes</item>
<item type="boolean" name="sl_CS">yes</item>
<item type="boolean" name="sl_CZ">yes</item>
<item type="boolean" name="sl_EE">yes</item>
<item type="boolean" name="sl_HR">yes</item>
<item type="boolean" name="sl_HU">yes</item>
<item type="boolean" name="sl_LT">yes</item>
<item type="boolean" name="sl_LV">yes</item>
<item type="boolean" name="sl_PL">yes</item>
<item type="boolean" name="sl_RO">yes</item>
<item type="boolean" name="sl_SI">yes</item>
<item type="boolean" name="sl_SK">yes</item>
<item type="boolean" name="sl_UA">yes</item>
<item type="boolean" name="sr_BG">yes</item>
<item type="boolean" name="sr_BY">yes</item>
<item type="boolean" name="sr_CS">yes</item>
<item type="boolean" name="sr_CZ">yes</item>
<item type="boolean" name="sr_EE">yes</item>
<item type="boolean" name="sr_HR">yes</item>
<item type="boolean" name="sr_HU">yes</item>
<item type="boolean" name="sr_LT">yes</item>
<item type="boolean" name="sr_LV">yes</item>
<item type="boolean" name="sr_PL">yes</item>
<item type="boolean" name="sr_RO">yes</item>
<item type="boolean" name="sr_SI">yes</item>
<item type="boolean" name="sr_SK">yes</item>
<item type="boolean" name="sr_UA">yes</item>
<item type="boolean" name="sv_DK">yes</item>
<item type="boolean" name="sv_FI">yes</item>
<item type="boolean" name="sv_NO">yes</item>
<item type="boolean" name="sv_SE">yes</item>
<item type="boolean" name="th_TH">yes</item>
<item type="boolean" name="tr_AT">yes</item>
<item type="boolean" name="tr_CH">yes</item>
<item type="boolean" name="tr_DE">yes</item>
<item type="boolean" name="tr_TR">yes</item>
<item type="boolean" name="vi_VN">yes</item>
<item type="boolean" name="zh_CN">yes</item>
<item type="boolean" name="zh_HK">yes</item>
<item type="boolean" name="zh_TW">yes</item>
<item type="boolean" name="defeault">en_US</item>
</set>

then replace the file on your phone with the one you just modded

THEN YOU MUST WIPE DATA TO SEE YOU LANGUAGE IN YOUR DEVICE SETTINGS

FOR SAMSUNG JUST USE WANAM LANGUAGE ENABLER APP FROM GOOGLE PLAY​