Moliere uses rhyming couplets in Tartuffe and each line of the play has the same number of syllables: twelve.

Moliere uses rhyme because this is a madcap, fast-paced comedy, and the rhyme scheme helps both actors and audiences remember the lines, which are spoken in quick succession. The rhyme imposes structure so that the play doesn't become too chaotic.

Translations, of course, can have a hard time replicating this rhyme scheme. It's best to read a work of literature in its original language, but as we all don't have time to learn every language fluently, we are forced to rely on translations. Some English translations try to capture the rhyme as far as possible, while others abandon that attempt and go for replicating the spirit, wit, and meaning of the original without rhyme.

Your question draws our attention to a very important aspect of this brilliant play that it is important not to forget. To put it simply, Moliere wrote this play originally in French, and therefore every copy that we read today in English has been translated from the original French. This of course means that a number of different aspects of the original play in its original form are going to be lost in translation. This becomes particularly relevant when we remember that Moliere wrote this play in French verse, with every line possessing twelve syllables and the lines organised into rhyming couplets (a form of verse known as alexandrine).

Translators have approached this issue in a variety of ways. Some have, for example, tried to stay faithful to the original and have translated the play into verse with rhyming couplets, as Richard Wilbur's translation did. In his case, he chose to dispense with the alexandrine form, however. Others dispense with verse and rhyme altogether, converting the play into prose.