Hundred Words: https://apps.apple.com/us/app/hundred-words/id1469449237
Language Pairs: https://itunes.apple.com/us/app/language-pairs/id1438817614?...
DuoLingo is probably the most widely used app.
https://www.duolingo.com/
Get somewhat proficient in basic vocabulary then travel. Immersion is the best way to learn but it helps to know some basic vocabulary.