Tolkien himself never translated this particular quote so you will get as many different ideas as there are translators, because it is by no means straight forward to puzzle out Tolkien’s intentions sometimes. I’d say:
Quenya/High-Elvish: lán quetuva “áva níta” an lá ilyë niër ulcë ná
Sindarin/Gray-Elvish: avon peded “avo nído” an egil law il nîn
However, this quote contains many much debated questions of Neo-Eldarin, such as: Is Ū or LĀ the root for verbal negation? What’s the grammatical difference between “not all tears are…” and “all tears are not”? What is the best way to form a neologism for “weep” from Tolkien’s roots? etc. so I would strongly advise against a tattoo of this in translated form. A safer variant would be to transliterate the quote into Tengwar without translating it. That means it would still be English, so you sidestep the complications of translations, all while looking pretty and “elvish” nevertheless. Such a transliteration would look like this. Feel free to play with the fonts (except Tengwar Formal, it has issues) but don’t change the mode drop down or the input text.