If I don't know the Arabic meaning of a Dua, can I say the Dua in a different language?
If the Du'a is within Salah, then I don't think you can translate it into your language.
But, if the Du'a you're making is after the completion of Salah, Of course Why not?
Yes it is highly suggested that you make Du'a in a language in which you understand in the beginning.
It is (highly) suggested that you learn the literal meaning of the Arabic words of the Du'a as soon as possible and slowly start making Du'a in Arabic understanding what you're saying.
Because the basic definition of Du'a is a way of talking to Allah which I bet you would prefer to do it by understanding the conversation.
May the creator guide us all.
In the name of Allah the most compassionate the most merciful
Muslims ought to say their prayers in Arabic not in other languages. But according to many of Shia Marjas (not all of them), (I am not aware of dear Sunni Marja’s), it would be permissible to say your dua in other language during your Qunoot, Marjas such as Ayatollah Khomeini, Khamenei, Bahjat, … consequently it is better to say the Qunoot in Arabic. As a result, you ought to say your all prayers in Arabic (except what I stated…)
As a suggestion, endeavor to learn the meaning of Salah sentence, it won’t be so hard or taking a lot of your time to learn them. (In order to have a better comprehension from the salah).
Duah (dua/prayer) is something personal between you and your lord, as you are supplicating to Him and asking from him. As long as it is from your heart and you know your place in front of your lord, no one can say what you are doing is wrong unless there is some Islamic law against it. To my knowledge i have never heard of any such ruling that duah should only be read in Arabic, but always think of duah as asking for a favour from your lord. You should however try to learn the Arabic language to try understanding the Quran, which in turn can also help with knowing how to recite duah in Arabic if that is an issue for you :) salaams