docs(completion): add additional language intro (#3355)

website/docs/administration/code-completion.md

@@ -1,8 +1,12 @@
 # Code Completion
 
-Code completion is a key feature offered by Tabby in IDEs/extensions. Tabby allows for more customized configuration by modifying the `config.toml` file in the `[completion]` section.
+Code completion is a key feature provided by Tabby in its IDEs/extensions.
+Tabby can analyze code repositories or documentation supplied by users
+and leverage them to generate helpful code suggestions.
 
-## Input / Output 
+Tabby also allows for more customized configurations by modifying the `[completion]` section in the `config.toml` file.
+
+## Input / Output
 
 This configuration requires tuning of the model serving configuration as well (e.g., context length settings) and can vary significantly based on the model provider (e.g., llama.cpp, vLLM, TensorRT-LLM, etc).
 Therefore, please only modify these values after consulting with the model deployment vendor.
@@ -19,3 +23,114 @@ max_decoding_tokens = 64
 
 The default value is set conservatively to accommodate local GPUs and smaller LLMs.
 
+## Additional Language
+
+Tabby supports several built-in programming languages.
+For more details, please refer to [Programming Languages](../references/programming-languages.md).
+
+Users can manually configure additional programming languages by defining them in the `config.toml` file.
+
+Below is an example of how to support Swift:
+
+<details>
+  <summary>Swift Additional Language Configuration</summary>
+
+```toml title="~/.tabby/config.toml"
+[[additional_languages]]
+languages = ["swift"]
+exts = ["swift"]
+line_comment = "//"
+top_level_keywords = [
+    "import",
+    "let",
+    "var",
+    "func",
+    "return",
+    "if",
+    "else",
+    "switch",
+    "case",
+    "default",
+    "break",
+    "continue",
+    "for",
+    "in",
+    "while",
+    "repeat",
+    "guard",
+    "throw",
+    "throws",
+    "do",
+    "catch",
+    "defer",
+    "class",
+    "struct",
+    "enum",
+    "protocol",
+    "extension",
+    "true",
+    "false",
+    "nil",
+    "self",
+    "super",
+    "init",
+    "deinit",
+    "typealias",
+    "associatedtype",
+    "operator",
+    "precedencegroup",
+    "inout",
+    "async",
+    "await",
+    "try",
+    "rethrows",
+    "public",
+    "internal",
+    "fileprivate",
+    "private",
+    "open",
+    "static",
+    "final",
+    "dynamic",
+    "weak",
+    "unowned",
+    "lazy",
+    "required",
+    "optional",
+    "convenience",
+    "override",
+    "mutating",
+    "nonmutating",
+    "indirect",
+    "where",
+    "is",
+    "as",
+    "new",
+    "some",
+    "Type",
+    "Protocol",
+    "get",
+    "set",
+    "willSet",
+    "didSet",
+    "subscript",
+    "fallthrough",
+    "Any",
+    "Self",
+    "unknown",
+    "@escaping",
+    "@autoclosure",
+    "@IBOutlet",
+    "@IBAction",
+    "@available",
+    "@dynamicCallable",
+    "@dynamicMemberLookup",
+    "@objc",
+    "@objcMembers",
+    "@propertyWrapper",
+    "@main",
+    "@resultBuilder",
+]
+```
+
+</details>