user define language

1. pre-defined language are in the folder path_to_install_dir\resources\app\extensions (my directory is D:\Programs\Microsoft VS Code\resources\app\extensions). one language is put in one folder.
2. find one pre-defined language, that is similar to yours. I use vb as my language basis.
3. make a copy of folder vb, rename the new folder as mylangw.
4. edit mylangw/package.json, rename every key named vb to mylangw. modify extensions value to yours.
5. modify contents in folder mylangw, to meet your demands. for example, one differance of mylangw to vb is the leading of comment line. I replace every ' in the the folder mylangw with //.

outline of new language

the extension codeMap support user define file outline.
CodeMap - Visual Studio Marketplace
https://marketplace.visualstudio.com/items?itemName=oleg-shilo.codemap

define file outline key

add the following code snippet to vscode's settings.json

"codemap.mylangwExtension0": [
    {
        "pattern": "F_\\w*\\(\\):",
        "icon": "function"
    }
],
"codemap.mylangwExtension1": [
    {
        "pattern": "F_\\w*\\(\\):",
        "icon": "function"
    }
],

format

Custom Format - Visual Studio Marketplace
https://marketplace.visualstudio.com/items?itemName=Vehmloewff.custom-format

ref

How can I implement my own code outline layout in vscode? - Stack Overflow
https://stackoverflow.com/questions/48306520/how-can-i-implement-my-own-code-outline-layout-in-vscode

vscode extensions - Create Custom Language in Visual Studio Code - Stack Overflow
https://stackoverflow.com/questions/30687783/create-custom-language-in-visual-studio-code

CodeMap - Visual Studio Marketplace
https://marketplace.visualstudio.com/items?itemName=oleg-shilo.codemap