You may go with him if you (so) choose.
行きたいのなら彼といっしょに行ってもいいよ
You may translate his statement as an admission of guilt.
彼の陳述は罪を認めたものと解釈してよい
you may well ask
((略式))（わけを）聞いてみたいもんだね
You may well believe it.
君がそれを信じるのももっともだ
You might as well expect a river to flow backward as hope to move me.
私の心を動かそうとするのは川の逆流を期待するようなものだ
You might as well give it away.
くれてやるようなものだ；あっさりくれてやったほうがいい
You might as well give up.
降参したらどうだ（◆「抵抗してもむだだよ」の含意がある）
You might just as well leave now.
そろそろ出発されてもよろしいでしょう（◆may as wellより丁寧）
You must be in 8th grade or under to participate in the Kids Club.
子どもクラブへの参加は８年生以下が条件だ
You must stand and fight or else flee.
立ち上がって戦うか，さもなくば逃げるかだ
