translating filter button label

Hi,

You should add your modification in the override area when you edit your translation file via the interface of the configuration like that:
FILTER="My custom text"

Could you do a screenshot of your modification ?

That's correct indeed.

Then, it must be joomla translation files overriding that override in some way.
In that case, you should edit the file "filter" for your front end template via the menu Display->Views and directly change the text :
JText::_('FILTER')

by:
'Rechercher'

and that will do what you want.

Then, you could replace JText::_('FILTER') by this:
JText::_('MY_FILTER')

and in your override file, you could do like that:
MY_FILTER="Rechercher"

That way, the Joomla override when mess with yours.