This Sublime Text 4 plugin provides the set_default_syntax_dialect command.

This command manipulates a syntax file (e.g.: SQL.sublime-syntax) to make it point to a desired dialect (e.g.: MySQL.sublime-syntax). As a result the dialect is used whenever the default syntax's scope (e.g.: source.sql) is addressed. This way it is possible to specify the syntax to use in embedded code blocks.

Syntax definitions may embed others to highlight certain parts of a document with that external language. Very popular examples are:

1. HTML embeds CSS and JavaScript.
2. Markdown embeds many other syntaxes to highlight fenced code blocks
3. Ruby/PHP embed various syntaxes (e.g.: SQL, XML, ...) to highlight HEREDOCs

They do so by embedding scopes (e.g.: embed: scope:source.sql).

But what if such a syntax has several dialects while the embedding syntax doesn't have any solution to distinguish them?

Ruby/PHP only know about "SQL" syntax. But SQL may be used as synonym for MySQL, PostgresSQL, SQLight or T-SQL.

A command for the target syntax is to be added to Default.sublime-commands

[
    {
        "caption": "Set Syntax Dialect: SQL",
        "command": "set_default_syntax_dialect",
        "args": {
            "syntax_file": "Packages/SQL/SQL.sublime-syntax"
        }
    }
]

The target syntax should be an alias and must be extended from a dialect.

%YAML 1.2
---
name: SQL
scope: source.sql
version: 2

extends: Packages/SQL/MySQL.sublime-syntax

file_extensions:
  - sql
  - ddl
  - dml

first_line_match: |-
  (?xi:
    ^ \\s* -- .*? -\\*- .*? \\bsql\\b .*? -\\*-  # editorconfig
  )