That sounds like Bug 1889697 which should be fixed in version 125. Try updating to the latest version.

Note that this is a problem with fonts and not a language related issue.

You can right-click and select "Inspect" to open the built-in Inspector with this element selected.

• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/open_the_inspector/
• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/examine_and_edit_html/

You can check in the Rules tab in the right panel in the Inspector what font-family is used for selected text. You can check in the Fonts tab in the right panel in the Inspector what font is actually used because Firefox might be using a different font than specified by the website. If the Fonts tab is hidden, click the Down arrow at the right end.

• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/edit_fonts/

Please disregard my previous comment, I did not see your screenshot. This is possibly due to Strict Tracking Protection limiting font visibility in private windows, try switching to Standard or Custom with "Suspected fingerprinters" disabled.