Hi Delphine.
I haven't any iOS devices and Mac. As result, I can only test Firefox Focus for Android.
I tested Firefox Focus for Android with Persian language on Android 5.1 ; it seams Firefox Focus isn't compatible with Android 4.4.2 because I couldn't install it on Android 4.4.2. It shows this error on Android 4.4.2 : "There was a problem parsing the package".
I should inform you that Firefox Focus for Android is fully compatible with RTL languages. Because the direction of sentences are true and there isn't any problem which is directly related to RTL compatibility.
But I found some bugs in the Firefox Focus for Android with Persian language that are not related to RTL directly. I reported them in Bugzilla:
In addition because SUMO is migrating to new CMS, it's bugs effected on Mozilla products such as Firefox Focus for Android when it's language is not English. For more info, you can look at these two bugs:
In addition, I should inform you that when I installed Firefox Focus on Android, it's name in main menu of Android is Focus (Beta) under it's icon. I found a bug in Bugzilla which said name of Focus should be change to Firefox Focus. I saw name of app in it's main screen and about page is Firefox Focus, I don't know if name of App under it's icon in Android menu is Focus (Beta), it's a bug or it' ok?
Suggestion: Please make two categories in Bugzilla, which named Focus for Android and Focus for iOS. Now in Bugzilla we have only one category named Focus. I selected it inevitably!
Thanks.
Amir.