Based on your comment:
The html generated by the widget? That one just shows the Strings in the _e function for eg: _e(“Category”) displays “Category”
I suspect that you’ve not configured your translation strings properly. You need to include the textdomain in every translation string function call, or else the strings will never get translated.
e.g. for your textdomain 'list-category-posts':
_e( 'Category' )
…should instead be:
_e( 'Category', 'list-category-posts' )
Ensure that all of your translation string functions are declared accordingly.