Since the topic of "subjectivity in language" is all new to me, I am looking for an introduction to the topic that 1) gives an overview of the phenomena usually associated with the topic (evidentiality? modality?) and/or 2) contains information on how subjectivity is expressed in different languages. Thanks a lot
A good introduction is Heiko Narrog's Modality, subjectivity, and semantic change. This link accesses the Japanese amazon site, where you can, if you're quick, have a look inside. Just click on the picture of the book cover in the upper left corner.
I think you'll probably find Alexandra Aikhenvald and her book on evidentiality a good starting point on the cross linguistic front.
But of course, subjectivity is much more complex than the associated morphosyntax. I think Ari Verhagen cognitive linguistic treatment of Intersubjectivity addresses many important issues related to the semantics and pragmatics of subjectivity.