The Welsh idiom, dros ben llestri (literally, “over (the) dishes/crockery”), means ‘over the top’, as in excessive, exaggerated or beyond reasonable limits. The phrase dros ben on its own means “residual, spare; extra, extremely, indeed, over”. I’m not sure how this phrase came to be associated with exaggeration.

In French there are a number of ways to express the same concept:
– (être) exagéré / trop / délirant(e) = (to be) over the top (excessive)
– encenser = to go over the top (praise excessively)
– en faire trop / en faire des tonnes / aller trop loin / dépasser les bornes = to go over the top (do sth excessively)

encenser also means ‘to praise by burning incense (l’encens)’.

Here are a few examples of usage:

– Votre réaction est exagérée = Their reaction was well over the top
= Mi aeth eu ymateb dros ben llestri

– L’Eurovision, c’est vraiment trop ! = Eurovision is so fantastically over the top
= Mae Eurovision yn hollol dros ben llestri

– Cette fois, il dépasse vraiment les bornes ! = This time he’s really gone too far / over the top!
= Y tro ‘ma, mae o ‘di mynd dros ben llestri yn wir.

The English expression over the top first appeared in print in 1965, and the acronym OTT made its first appearance in 1982 in the Official Sloane Ranger Handbook, according to the OED.

Sources: WordReference.com, OED

How do you express the same idea in other languages?