How do I say.. "I forget how to say this in Japanese"?
Whenever I am speaking in a conversation in Japanese, I always end up trying to reply to someone but then I forget the phrase or word.

I want to tell them. "Uggh I forget how to say this in Japanese!" or "I forget the word in Japanese"

IS 日本語で言葉は忘れます? correct?
or 日本語で言葉は忘れるし増す?
or should I use a completely different phrase?

Thanks for your help!

Question

How do I say.. "I forget how to say this in Japanese"?
Whenever I am speaking in a conversation in Japanese, I always end up trying to reply to someone but then I forget the phrase or word.

I want to tell them.  "Uggh I forget how to say this in Japanese!" or "I forget the word in Japanese"

IS 日本語で言葉は忘れます?  correct? 
or 日本語で言葉は忘れるし増す? 
or should I use a completely different phrase?

Thanks for your help!

Answer

I forget how to say this in Japanese!
これを　日本語で　      　なんていうか　忘れた。
this　　　in Japanese　how to say　　forget

I forget the word in Japanese.
その日本語を　         　忘れた。
the Japanese word　forget

Hope this answer helps you.

Answer

[casual]
「あー、日本語でなんて言うか忘れた！」[aa, nihongode nanteiuka wasureta!]
[polite]
「日本語でどういうのか忘れました。」[nihongode douiunoka wasuremasita.]

Or, if you want to say like, " how can I say..."  like speaking to yourself,
you can say,
「なんていうんだっけ、、、」[nante iun dakke]