@wpaiksas,
In general it’s best to not post into old threads created by other people and that have already been set to resolved.
I do not recommend modifying the recent-posts.php file directly. To start with, if you edit any theme file directly, those edits will be lost the next time the theme updates. But it also runs the risk of completely breaking your site if you’re not careful. If you want to make changes to a theme file, the recommended method is to do so using a child theme:
https://developer.www.ads-software.com/themes/advanced-topics/child-themes/
But the better option here is to translate the theme.
All strings included in this theme is translatable, including the Recent Posts string. Looking at the translation project for this theme at https://translate.www.ads-software.com/projects/wp-themes/ixion/fr/default/ the Recent Posts string has already been translated to French, but it looks like it’s waiting for a validator for French to approve those changes before it will be available to use.
You can try reaching out to a translation editor for French to ask if they can review and approve those translations. You can find the translation team for French at https://make.www.ads-software.com/polyglots/teams/?locale=fr_FR – just keep in mind that like everyone here they’re volunteers who do this in their free time.
Once a translated version of the theme is available, your multi-lingual plugin should be able to take care of displaying the correct language version of the theme as needed.