dict.cc dictionary ( iOS / Android ): 51 language combinations, usable without internet connection (offline dictionary)
Dictionary Linguee ( iOS / Android ): answers to your most difficult queries.
iTranslate ( iOS / Android ): over 90 languages, can translate dictation, a feature to slow down audio playback, thereby helping eliminate pronunciation errors.
Google Translate ( iOS / Android ): free for over 100 languages, with a feature that allows you to take a photo of signs and have the text translated instantly, you can also download common phrases in the event that you have to travel to places with no internet service, about half of the languages can be translated using no internet service at all.
LEO dictionary ( iOS / Android ):
TripLingo ( iOS / Android ): free version offers basic access to 23 languages, geared toward travelers, offers several translations of phrases, even slang translations.