It's okay that I'm not that good at English. I don't really care.
I know I'm pretty bad at English, but it's not that big a deal.
ーIt's okay that I'm not that good at English. I don't really care.
「英語が下手でもいいじゃん。気にしない」
not that good at ... で「…があまり上手くない・得意でない」
ーI know I'm pretty bad at English, but it's not that big a deal.
「英語が下手なのは知ってるけど、大したことじゃない」
bad at ... で「…が下手で」
it's not that big a deal. で「大したことじゃない」
ご参考まで!