ALCESTE: This is a subject on which, no matter what is learned, doubts are more cruel than the worst of truths.

[Mais sur ce sujet quoi que l’on nous expose,
Les doutes sont fâcheux plus que toute autre chose.]

Molière (1622-1673) French playwright, actor [stage name for Jean-Baptiste Poquelin]

Le Misanthrope, Act 3, sc. 7 (1666) [tr. Wormeley (1894)]
    (Source)

On being told by Arsinoé that he is betrayed by Célimène.

The scene breakup for Act 3 varies in different translations, as indicated. (Source (French)). Alternate translations:

But whatever may be openly said on this subject is not half so annoying as hints thrown out.
[tr. Van Laun (1878), 3.7]

But on this subject, whatever we may be told, doubts are of all things the most tormenting.
[tr. Matthew (1890) 3.4]

But whatever we may be told on this subject is not half so disturbing as hints and innuendoes.
[tr. Waller (1903), 3.5]

In such a case, whatever we may learn,
Doubts are more torturing than any truth.
[tr. Page (1913), 3.7]

Madam, you know that doubt and vague suspicion
Are painful to a man in my position.
[tr. Wilbur (1954), 3.7]

No matter what one says on such a theme,
It's doubt which is the most distressing thing.
[tr. Bishop (1957)]

Whatever we are told in this domain,
Doubt is the thing that gives the greatest pain.
[tr. Frame (1967), 3.5]