Should I do anything when I see several references that are not used in the text? In a linguistics paper I read, I noticed that several references in the bibliography are not actually used in the text. This is for about 10-15% of the references the case. Should I do anything with this?
I always thought that all references must be used in the text, because even if they are just suggestions for further reading you would want some explanation why it is relevant and what you can find where. 

I only know the author through their work and do not know the editors. The paper is from 2011. The references are rather general. They are relevant to the paper, but you would want page numbers with them unless you are familiar with them. They are all from different authors and different institutes. It is likely that the references were used in previous versions of the text.
There's nothing inherently wrong with this.  It's sometimes done to mention sources that provided general background information, or that the author suggests for further reading, but which weren't needed to support any specific claim within the paper.  Some journals don't allow this, but it's a matter of style. 

Even if the journal didn't want this, or if those references were included by mistake, it's a harmless error which just wastes a little bit of space.

If you have good reason to suspect that references were given in bad faith purely for padding, or to increase citation counts of other articles, then that would be misconduct - whether they were cited in text or not.  But otherwise I don't see that this represents anything improper, and there is nothing you should do about it.