Improve RTL languages support

[jacopofar]

See https://isthisarabic.com/

Using Arabic as a target or source language the text is still aligned to the left. It seems the option dir="rtl" on the sentences can adjust it, investigation is needed to check whether it's enough.

[Yorwba]

FYI, here's how Tatoeba decides which value for dir to use: https://github.com/Tatoeba/tatoeba2/blob/f1dd80e9280937e1f4b32ef276f4fdea842adb4e/src/Lib/LanguagesLib.php#L640

[jacopofar]

Thanks! I'll also have to pass the ISO code to the frontend, at the moment it receives only the language name (in English) to display

[jacopofar]

Added dir support using the same method, still have to check the rest of the problems listed in that site