For more accuracy, the first sentence could be reworded as follows: هل الجملة التالية صحيحة؟ You begin with the wh-question word 'هل', main noun ’الجملة’, adverb ’التالية’, then adjective ’صحيحة'. The second sentence is grammatically correct. It means ’I will feel happy after I study Arabic’. But if you would like sound more like a native speaker. You may say: أشعر بسعادة عندما أدرس اللغة العربية It exactly means: ’I feel happy when I study Arabic’.