Add a lang=“fi” attribute to your a.twitter-timeline fallback content for interpretation by Twitter’s JavaScript when rendering the page. If a parent element in the DOM declares a lang attribute the Twitter JavaScript should inherit that language context.
<a class="twitter-timeline" href="https://twitter.com/{screen_name}" lang="fi" data-widget-id="{widget_id}">
or
<html lang="fi">
...
<a class="twitter-timeline" href="https://twitter.com/{screen_name}" data-widget-id="{widget_id}">