If a theme supplies font size values that are variable they are represented as a 1 - x scale on the control:

This is perhaps suboptimal:

• The most intuitive label is hidden in a tooltip
• The labels in the control feel arbitrary. Are they associated with units? Is "1" small or large?

In #34345 (comment) 'Tshirt sizing' was suggested as an option:

Assuming it works from an i18n perspective it would be good to try implementing this as it solves the issues above, and feels more familiar.