How common is it cross-linguistically for a language to have a different word order in various types of embedded clauses such as relative clauses?
WALS appears to collect information on word order in matrix clauses, but not specifically on various kinds of embedded clauses. Here are some examples of what I'm talking about from a fairly diverse group of languages.
[bɨryekomo komo yonyetxkonɨ] kamara [txetxa wawo] amnyehra child.COLL COLL 3s3o.eat-coll-distpst-cont jaguar forest in long-ago The jaguar used to eat children in the forest long ago.
In nonmatrix clauses it is SOV. I don't know the order of the oblique in non-matrix clauses in Hixkaryana, but I suspect it is SXOV. I'm still combing through the thesis for relevant examples.
Also, some languages such as German have V2 word order in matrix clauses and SOV word order in embedded clauses. Although in other Germanic languages, the embedded clause word order is SVO.
This article on Luganda mentions that in passing that several other Bantu languages besides Luganda invert the subject and verb and use a dedicated attributive verb form indicated with prefixing to form relative clauses.
This is somewhat unusual – the more well-known pattern in Bantu is for the relative marker either to be an ‘independent word’ preceding the subject, or a prefix on the verb with subject-verb inversion (Demuth and Harford 1999).