Instant translation removed the main friction in language learning, and friction was doing some of the work. The tools are genuinely useful. The question is whether a lookup leaves anything behind.
A single-word lookup teaches the least
Most words have several translations and the dictionary gives you the first one, which is right about half the time. Words also mean different things in different collocations. Look up the phrase, not the word. Search the expression in quotation marks and look at how it appears in real sentences; that shows you usage, not just meaning.
Translate out, then check, rather than translating in
Writing your sentence yourself and then checking it teaches you something. Typing your idea into a translator and copying the result teaches you nothing, because you never had to build anything. The order matters more than the tool. Produce first, verify second.
Machine translation is confident when it is wrong
It handles ordinary prose well and quietly mangles register, idiom and anything culturally specific. It will give you a grammatically perfect sentence that no one would say. Treat its output as a draft by a fluent stranger who has never met the person you are writing to.
Make the lookup cost something
A word you looked up in one second and never used is gone within the hour. Say the word aloud in a sentence of your own before you close the tab. If you look the same word up three times, that is the signal to learn it properly rather than look it up a fourth.
Use the tools freely, in the right order: produce, then check, then say the result out loud. Looking something up is not the problem; looking it up instead of building it is.