as for social media I used to use Wechat When I was studying Chinese but since I focused on learning English Kakaotalk became the app I use the most.
Plz correct this sentence if there is something wrong 用 英語 (英國) 要怎麼說？

查看翻譯

Hello! There is nothing wrong with this sentence and it is entirely grammatically correct, so good job :) The only problem would be punctuation. Here is my suggestion:

“As for social media, I used to use Wechat when I was studying Chinese but since I focused on learning English, Kakaotalk became the app I use the most.”