The current language of your topic sets the language of all your search queries.
Here’s a little trick to change it:
1. On your Curate page click on Manage> Edit> then set your language in the dedicated field. Don’t forget to click on Save.
2. Remove your current Twitter source with lang=EN. In order to do so click on Manage> Manage Sources> click on the red “-” to delete a source.
3. In Manage Sources click on the Advanced Options tab then add your Twitter source.
Now the language of your Twitter search is modified!
Note: You can always change back the language of your topic to the former one.