お姉さんは僕と同じでビデオゲームが好き、でも僕とちがって日本語勉強することじゃなくて中国語勉強する。(edited)
Translation:
My older Sister likes Games like me, but unlike me she does not learn japanese, but chinese.
So, regarding leaving things out, as this is a problem for myself as well:
Could I leave out the second 「僕」 and the second 「勉強」?
@Klaboon @matt_in_mito
Hope pinging you is fine with you
edit: thanks @matt_in_mito for the correction.
するじゃなくて is wrong, because ではなくて and variations are constructs that can’t come directly after verbs.