[Xperia Z3 Compact General] pakjebakmeel:
An attempt to figure this out myself, I have extracted 2 firmwares from the same version:

D5803_23.0.A.2.93_Customized_FR

D5803_23.0.A.2.93_Generic_GLOBAL

This are the differences I found:

This doesn't tell me the actual differences but it gives me an idea of what files are affected between customization versions. On important thing I noticed is that the French version has Fast Dormancy enabled in config.prop:

######################## Customized property values #########################
ro.semc.enable.fast_dormancy=true
ro.nfc.icon.enable=true
ro.semc.ecclist.num=1
ro.semc.ecclist.number.0=112
persist.ro.ril.sms_sync_sending=1
ro.product.locale.language=fr
ro.product.locale.region=FR
ro.telephony.default_network=9
ro.cst.prm=1288-6117:R12B
#############################################################################

The Global version does not:

######################## Customized property values #########################
ro.product.locale.excluded=ALL_Languages_Please
ro.telephony.default_network=9
ro.cst.prm=1286-9917:R9B
#############################################################################

I think not all providers support fast dormancy so the customized versions for specific countries will have it enabled. The generic version might not have it. So, it seems there ARE some functional differences between builds we should be aware of. I'm going to investigate further and see if I can find other functional differences.

At a glance:

- Fast Dormancy (http://androidforums.com/threads/fast-dormancy-in-a-nutshell.674208).

- Global version has less bloat (Kobo Books, Gameloft).

- French version has some overlays (take precedence over standard files). Yet to discover what the diffs are.

I'm going to stick to the Customized version for my country until I get more details

UPDATE:

- Global version has the browser app, FR doesn't. I assume this is AOSP browser?

- Global has the Panic Attack app, I presume some personal protection panic button app.

- Global has Roaming Genius, looks like some app to reduce data usage when roaming.

- NFC icon seems to be enabled in Global.

- French has SpecialOperatorStk, looks like some customized sim toolkit for local operators.

- Global has normal sim toolkit.

- French has BrowserProviderProxy, not sure what it does.

- Google TextToSpeech preinstalled on Global.

- French has more bloatware, gameloft, kobo books and sony diagnosticslauncher.

- Different config.prop, french has fast dormancy enabled global doesn't.

- Different notice.html.. Probably disclaimer or something that is localized.

- Overlays for browser differ, no idea what changed.

- Phone overlay seems to enable noise reduction and sets preferred network mode (to what? no idea.) for French by default. Does not exist in Global.

- Partnerbookmarks, only 1 character difference. Don't think anything really changed.

- French set Config.DefaultLocale and Config.EditableTetherDUNAPN. Not sure what it does.

- Social phonebook, French sets Enable.SpeedDial and SpeedDialMaxNumber. Probably increases or limits the number of speeddials.

- SonyEricsson capabilities, some differences. Can't tell what they are.

- French set DeliveryReportMMSMaxSize, probably limits MMS size somehow.

- French set CustomSettingsApptray and CustomSettingsDesktop for Sony Home. Not sure what it does.

- InitialBootSetup overlay sets default local in French version.

- R2R client has an overlay, not sure what the diff's are.

- SetupWizard has an overlay in French. It sets ConfigShowInternetSettingsScreen.

- Sony TrackID minor differences. Probably regional.

- UpdateCenter has an overlay in Global. It sets URLs for updates or tracking and puts app groups for whatever reason.

- SuperStamina, Global has an overlay that changes OperatorWhiteList whatever that does.

- French has Use4GInsteadOfLTE. You get 4G icon, not LTE I presume.

- Same as above but change the drawables aka the icon images to 4G.

- TeleService has an overlay in French. I think it might add APN's or recognition for local providers.

- Build.prop obviously differs.

So, my conclusion is that the different versions are quite close but they might have some important differences like fast dormancy, maybe APN's, recognition for local providers, 4G vs LTE icon, bloatware/apps added or missing and maybe some functional differences.

I'm done checking this, I will stay on my regional version to avoid carrier or similar problems. Hope this helps someone, I couldn't find this answer anywhere..

Thanks guys