I disagree with the question's proposed solution: a synonym from sql-server to t-sql.
I am also going to disagree with the quoted text. This is wrong:
Transact-SQL is central to using Microsoft SQL Server. All
applications that communicate with an instance of SQL Server do so by
sending Transact-SQL statements to the server, regardless of the user
interface of the application.
While it is technically accurate, the 'interfaces' used are often abstracted enough for the
t-sql to be invisible (think linq).
If there is to be a synonym, I believe the right one is to harmonize the SQL Server world with the other RDBMS's, and to synonym t-sql to just sql. Then, questions about SQL can all be tagged sql, and if the RDBMS is significant, it can be tuned with whatever back-end is relevant (oracle, mysql, etc.).
This allows for some questions to be tagged sqlsql-server, and others to be tagged linqmysql, and so on.
Synonym sql ← t-sql
Many questions already have the sql tag but not all, so that's not a problem. The issue is that many t-sql questions do not have sql-server.