This is somewhat similar to T311539: Gadget to move [edit] link does not align with [subscribe] link in Discussion Tools, except that it does not involve a gadget. The [edit source] and [subscribe] buttons are not aligned. The Subscribe button is higher.
(This screenshot was made from https://vi.wikipedia.org/wiki/Th%E1%BA%A3o_lu%E1%BA%ADn_Th%C3%A0nh_vi%C3%AAn:Bluetpp?safemode=1 in Chrome. Pale orange lines mark the baselines for the two labels.)
The same problem can be seen in Chrome, Firefox, and Safari. The same problem is seen in Vector and Vector 2022. A different problem appears in Monobook. The alignment is the other way around, and the colors are weird:
