We have to maintain layout as stable as possible. Considering that potentially there are approximately 7000 languages only following ISO 639-3 (even if we would like to see them all, in particular those in extinction, we will very likely have much less).
This means that the UI needs to be localized in many, many languages and this again means that if we used text we will get in layout-trouble.
So even if we are using text during the discussion of the UI, as much as possible on the UI must become graphical, that is using symbols and buttons with symbols. Text about the function shall show up by hovering over that symbols and buttons. Some like forward/backward are well known and established anywhere. Others are already used in translation environment and even more will need to be designed from scratch.