I suppose you're referring to online subtitles?
Did you already set your preferred subtitle language(s)?
Tap on menu
(while playing a movie, tap screen and then menu is at top-right in the bar).
Then tap on "Preferences" > "Subtitles" > "Online subtitles"
Now tap on "Online subtitle languages" and insert "ara" for general arabic
(Maybe add more codes, separated by a comma:
ISO 639 code sets.)
Finally tap "Select subtitle language", scroll down and select Arabic + tap [OK]
P.S.
1:
Note under "Select subtitle language" it is possible to select more than one language. Therefore perhaps look a bit further there and verify that no other (preferred) languages are set already, like perhaps "English", which you might want to untick.
P.S.
2:
If you're using LAN mode and you already have downloaded subtitles in several languages (or want to download new/further ones) or if you want to switch active language:
Tap screen > tap menu (at top right) > tap Subtitles (top of the list) etc...