I haven't spoken much Chinese lately, so I'm loosing it little by little.
I haven't had many opportunities to speak Chinese these days, so it's getting worse and worse.
この場合、次のような言い方ができますよ。
ーI haven't spoken much Chinese lately, so I'm loosing it little by little.
「最近あんまり中国語を話してないから、だんだん忘れてきた」
to lose には「能力を失う」という意味があるので、ここでは中国語を話す能力を失う＝中国語を忘れる、という意味になります。
ーI haven't had many opportunities to speak Chinese these days, so I'm forgetting it gradually.
「最近中国語を話す機会があまりなくて、だんだん忘れてきた」
be forgetting を使う場合は、このように言えますよ。
ご参考まで！
I haven't used Chinese in a while so I've been forgetting it more and more.
"最近中国語を使っていないからだんだん忘れてきてしまった"
- I haven't used Chinese in a while so I've been forgetting it more and more.
- I haven't been using Chinese recently so I've forgotten a lot of it.
- My Chinese has gotten worse because I haven't used it much lately.
- I've forgotten a lot of Chinese because I haven't used it in a while.
カナダ 
アメリカ合衆国 
