Language overrides conflicts

-- HikaShop version -- : 2.3.3
-- Joomla version -- : 3.3.4

I use Hikashop on a multilingual site.
The override function is great and works fine with 2 languages, english and french.
But it doesn't work with spanish, really strange.

When I set the overrides in Hikashop -> Configuration -> Languages, it looks OK. Overrides are still here after saving.
But the frontend doesn't take the overrides for this language only.
In Extensions -> Language Manager -> Overrides, I do see my overrides for french and english, but not for spanish.
Then if I go back to Hikashop -> Configuration -> Languages, my spanish overrides are gone.

That's so weird. This problem happens with 2 websites, one using Joomla 3.3.2 with Hikashop 2.3.2, the other using Joomla 3.3.4 with Hikashop 3.3.3.

Hi,

I tried to override my translations via the Joomla interface and indeed, I see the change in the Hikashop interface.
What is really strange is that I can do it in both way with english and french (changes made in Hikashop interface are reflected in the Joomla interface, and vice versa). But it's not the case with spanish.

The thing is, that I have a lot of overrides to write and the Joomla interface is not really convenient.
Editing the file es-ES.override.ini in language/overrides folder doesn't work, I don't know why.

So it's probably a Joomla issue.
Thanks for your help anyway