The play was (and still is) so popular that it has been produced in many different countries.
Alas, the play is a real challenge for a translator, well not the whole play but its title. The title is a pun. It refers to being Ernest, as a name, as well as to being earnest as a mental quality.
Unfortunately, puns are very hard, even impossible, to translate to other languages. After all, this pun is based on two completely unrelated words being pronounced the same way in English and English alone. Yet, the pun is essential to the plot of this play, so it cannot be skimmed over by the translator.
I do not know how translators solved the dilemma in various other languages, I only can tell what they did in Slovak. The translator used a completely different name, namely Philip. And no, it does not sound like another Slovak word.
But, there is a Slovak expression, to have Philip. It means to be smart. The origin of this expression is not 100% clear, but, apparently it has something to do with Philip the Macedon being very smart, bright, and intelligent.
So, the Slovak translator of The Importance of Being Earnest named the play How Important It Is to Have Philip. And, of course, he replaced all occurrences of the name Ernest in the lines of the play with Philip.
I saw the play several times in Slovakia, I saw the movie as well, and I never realized the English original used a different name (and verb - to be vs. to have). Only after I left Slovakia and lived in Rome, I was trying to mention the play in a conversation with my American friend. It was then that I realized the play had to have a different title in English. Luckily, my friend was able to figure out quickly what play I was talking about when I explained what having Philip meant in Slovak.