It is explained by the steps to reproduce.
1) Go to the title screen and make a note of the yellow writing.
2) Click Singleplayer/Multiplayer/Options/Language Selection. Then click Done/Cancel and the yellow writing doesn't change (for me, at least).
3) Repeat step 2, but instead of clicking Done/Cancel, press Esc. The yellow writing changes.
Additionally, if you click Minecraft Realms from the title screen, clicking Back or pressing Esc won't change the yellow writing. Finally, as well as affecting the yellow writing, this affects the landscape on the title screen. Whenever the yellow writing changes, the animation resets to the beginning, but the animation continues from wherever it was when the yelllow writing doesn't change.