Is this natural? and where should I put "sometimes" in this case?

"In HiNative, the answers about Japanese for foreigners are also helpful to Japanese me sometimes."
「HiNativeでは外国人に向けた日本語についての回答も、時々勉強になる。」

質問を翻訳

Your sentence is understandable, but might sound more natural like this:
"On HiNative, the questions answered about Japanese for foreigners are also helpful to me, a Japanese, sometimes."

You could also put "sometimes" in these places:
"Sometimes on HiNative, the questions answered about Japanese for foreigners are also helpful to me, a Japanese."
"On HiNative, sometimes the questions answered about Japanese for foreigners are also helpful to me, a Japanese."