Localization of numeric/monetary data

When developing a medium to large project, there is a problem with localizing numeric/money data. In this note, I will talk about the difficulties of using the Symfony framework, Sonata Admin Bundle, and the client-side. But first, let's discuss the essence of the problem, as it is not very obvious at first glance.

So, let's say we have a project that renders numeric/money data on the server side (php/template engine). They should be displayed according to the set locale. The user can enter data (in their own representation). At the same time, the data can be processed on the client side (javascript). For example, in most European countries, except for the UK and Ireland, the decimal separator is a comma while in the UK and Ireland it is a period. Naturally, a user from Germany will enter data with a comma separator.