The SimpleLocalize web UI is not accessible. This is no longer acceptable under EAA (https://commission.europa.eu/strategy-and-policy/policies/justice-and-fundamental-rights/disability/european-accessibility-act-eaa_en)

There is too much wrong to go into here. Most urgently you need to make all interactive elements. This means removing tabindex="-1" from interactive elements (no idea why you would add that). Use native elements where they exist to get the a11y benefit e.g. Dialog elements, button elements (like in filters).

Add correct aria links between CTAs and their popovers. Using the native implementation will again help here.