Translate more system apps

[Zac0511]

At the moment, only Puter's main UI is translated, but the system apps (except settings and task manager) are not translated, like the file explorer, app center, dev center, notepad, etc...
They should be translatable too, and could be added to the translation files.

[AtkinsSJ]

File Explorer can use the same system we already use for translation.

The others though, are iframe apps, and that means they can't access the usual i18n() function. Maybe we could add an SDK function for it though.