Webflow allows you to include styles within plain text from this menu:
Webflow introduces a span to which it applies the style. With Polyflow it is currently not possible to apply styles to these spans, so if you need to add styles within text (bold, italics... ) you will have to create that text as rich text and not plain text.
On the other hand, if you have for example colour styles applied to plain text, you can create this element in Webflow, one for each language, translate it in Webflow and apply the "polyflow-only" attribute. Here you can see how to use the attribute: