I lol'd at はい、上手です, and it just got funnier from there.
Japanese Language
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Remember that you can add furigana to your posts by writing ~{KANJI|FURIGANA}~ like:
~{漢字|かんじ}~ which comes out as:
{漢字|かんじ}
すみません、私はまだ日本語があまり上手ではありません。
あざっす
I like this article's suggestion: https://japaneselevelup.com/the-best-response-to-nihongo-wa-jouzu-desu-ne/
tl;dr: 日本が好きですから!
Personally, I usually deny it:
いや、忘れてます!
いや、まだまだです!
And then say something ironically difficult:
片言だけですよ!
最近使っていないからレベルが衰えています。
Because it's entertaining.
Edit: formatting
I just say ありがとうございます and walk off sad