I installed a language pack of French of mageplaza it is successfully installed using composer and on my website language switcher is working fine but the issue is when i am changing the text that was still remaining to translate into french so i created fr_FR.csv into
app/design/frontend/Theme/demo/i18n
for testing it is working or not i tried to change 'Add to Cart' that is already translated to 'Ajouter au panier' so i changed it to csv to 'Ajouter au panier test' but not changing.
I did cache flush and deploy content too.