if you can't beat them, join them

English

If one's adversaries are stronger, it is better to join their side.
- 1985 August 24, “Will You Marry Me? (personal advertisement)”, in Gay Community News, volume 13, number 7, page 17:
  GWM seeks gay female for liberal marriage. If you can't beat them, join them!

if your adversaries are stronger than you, it is better to join their side

Chinese:
Mandarin: 如果打不過他們，就加入他們 / 如果打不过他们，就加入他们 (rúguǒ dǎ bùguò tāmen, jiù jiārù tāmen)
Finnish: jos et voi voittaa heitä, liity heihin
French: il faut savoir hurler avec les loups (one must know how to howl with wolves)
German: man muss mit den Wölfen heulen (de) (one should howl with wolves)
Korean: 이길 수 없다면 합류해라 (igil su eopdamyeon hamnyuhaera)
Norwegian:
Bokmål: kan du ikke slå dem, bli med dem
Portuguese: se não pode vencê-los, junte-se a eles
Russian: не мо́жешь поби́ть, присоединя́йся к ним (ne móžešʹ pobítʹ, prisojedinjájsja k nim) (literal), с волка́ми жить — по-во́лчьи выть (s volkámi žitʹ — po-vólčʹi vytʹ) (to live amongst wolves, you should howl like a wolf)
Spanish: si no puedes contra el enemigo, únete a él
Thai: ถ้าสู้ไม่ไหวจงเข้าร่วมซะ (Tha Su Mai Wai Chong Khao Ruam Sa)
Turkish: bükemediğin eli öp başına koy.

Gregory Y. Titelman (1996) Random House Dictionary of Popular Proverbs and Sayings', →ISBN, page 159
“if you can't beat them, join them”, in Collins English Dictionary.