Valo fonts don't look right with eastern letters

Hello all,

I use a language with accented letters but they are shown as bold and it looks ugly. (Vaadin 8.11)

I inspected the fonts in the Firefox and it shows that two different fonts used for the text in the image: Open Sans for the english text and Free Sans for the accented letters which looks bold.

What is the reason for this and how can it be fixed? What fonts are “included” with Vaadin 8?