devil is in the details

English

In allusion to God is in the detail.

(the) devil is in the details

(idiomatic) The specific provisions of, or particular steps for implementing, a general plan, policy, or contract may be complicated, controversial, or unworkable.
- 1998, Alain L. Sanders, "Israel: Let the People Speak," Time, 16 Dec.,
  The country has developed a strong consensus for peace, but the devil is in the details over what concessions should be made.

"Detail" as a mass noun is also used instead of "details" - The devil is in the detail.

specific provisions of something may be complicated

Chinese:
Mandarin: 關鍵在細節，細節決定成敗, 关键在细节，细节决定成败 (guānjiàn zài xìjié, xìjié juédìng chéngbài)
Danish: please add this translation if you can
Dutch: de duivel zit in de details
Finnish: piru asuu yksityiskohdissa
French: le diable est dans les détails (fr)
German: der Teufel steckt im Detail
Greek: ο διάβολος κρύβεται στις λεπτομέρειες (o diávolos krývetai stis leptoméreies)

Italian: il diavolo è nei dettagli, il diavolo si nasconde nei dettagli
Japanese: 悪魔は細部に宿る
Polish: diabeł tkwi w szczegółach (pl)
Romanian: teoria ca teoria, dar practica ne omoară, socoteala de acasă nu se potrivește cu cea din târg, dracu-i în amănunte ascuns.
Russian: гла́дко бы́ло на бума́ге, да забы́ли про овра́ги (gládko býlo na bumáge, da zabýli pro ovrági) (rhyme: it was smooth on paper, but the ravines were forgotten)
Spanish: el diablo está en los detalles
Swedish: djävulen sitter i detaljerna
Turkish: şeytan ayrıntıda gizlidir