Verify translatable strings

[r-akemii]

It would be ideal to:

• check if all strings marked as translatable are indeed necessary;
• check if all localized strings are being translated in Transifex;
• check if all strings translated with Transifex are "placed" in the right spot;
• check if there are any missing strings to be localized;
• update Transifex translation documentation;
• add a subsection with formatting good practices for translatable strings.