AIP-4231: more inclusive language

Author: vchudnov-g

aip/client-libraries/4231.md

@@ -58,7 +58,7 @@ message Topic {
     when building resource name strings.
   - Variable substitution names are usually specified in `snake_case`, but this
     is not guaranteed. Client libraries **should** be able to accept any
-    annotation that uses any sane case system.
+    annotation that uses any coherent case system.
   - Patterns are usually slash-separated, but this is not guaranteed. Client
     libraries **should** use string interpolation to piece together the
     resource name.