言ってはいけない

must not say

→ 言う
phrase Rare #20,112
must not say Expresses a prohibition: something should not be said or mentioned. It is formed from the te-form of 言う (to say) plus はいけない (must not).
JA: そんなひどいことを言ってはいけない。
EN: You must not say such terrible things.

死んだ人たち悪く言ってはいけない

You shouldn't speak ill of the dead.

うそ言ってはいけない

You must not tell lies.

その事を両親に言ってはいけない

You mustn't tell your parents about that.

いないところでの悪口絶対に言ってはいけない

You should never speak ill of someone behind their back.

その人のいないところで悪口を言ってはいけない

You shouldn't speak ill of someone behind their back.

トム酔っ払って言ってはいけないことを言ってしまった

Tom got drunk and said something he shouldn’t have.

食べ物不平を言ってはいけない

You must not complain about the food.

クラスメート悪く言ってはいけない

You must not speak ill of your classmates.

そんなことを人前で言ってはいけない

You shouldn’t say things like that in front of other people.

ジムのいないところで悪口を言ってはいけない

You mustn't speak ill of Jim behind his back.