Add lang-selection string to all locales

In gh-110 lang-selection string was added only to ru-RU locale.
  This resulted in erroneous (Russian) string being shown for other languages, when
  either:
    a) User selected "ru-RU" from select box;
    b) User had "ru-RU" locale set-up in browser and opened any asknot page,
       including visits from permalinks.

Solution is quite straightforward - include lang-selection string for all locales.

As I am obviously not proficient in all changed languages, translations were taken from:
  http://transvision.mozfr.org/string/?entity=browser/chrome/browser/preferences/languages.dtd:languages.customize.selectLanguage.label&repo=central
  http://transvision.mozfr.org/string/?entity=mobile/android/chrome/localepicker.properties:chooseLanguage&repo=central

For Asian/Arabic/non-Latin script locales there is sadly no translation available,
  and it is left to corresponding translators to fix this one up.

Closes gh-71
Fixes gh-111

Signed-off-by: Aleksandrs Ļedovskis <aleksandrs@ledovskis.lv>
Append Firebug project into the list
Update zh-TW strings
Merge pull request #117 from janodvarko/master

Append Firebug project into the list
Merge pull request #116 from aledovsky/chore/lang-selection_update

Add lang-selection string to all locales
Merge pull request #118 from petercpg/patch-1

Update zh-TW strings
Update and improve zh-CN strings
Merge pull request #119 from yfdyh000/patch-1

Update and improve zh-CN strings
Add Latvian (lv) translation

Signed-off-by: Aleksandrs Ļedovskis <aleksandrs@ledovskis.lv>
Merge pull request #122 from aledovsky/feature/lv-LV_translation

Add Latvian (lv) translation