feat: translate doc to en, add index files

docs/en/stdlib/builtins.md

@@ -0,0 +1,20 @@
+# Built-in functions
+
+FZLang provides built-in functions that are available in every program.
+
+## Exit: `exit`
+
+```
+fn exit(uint code)
+```
+
+Takes an unsigned integer argument and exits the program with the specified code.
+
+## Print to stdout: `printline`
+
+```
+fn printline(value)
+```
+
+Accepts any value and writes it to standard output. Primitive values are printed directly according to their types. Objects are printed as `obj<...>`, where `...` is a list of their field values. Each field is printed with its type and value in the format `T<V>`, where `T` is the type name and `V` is the current value.
+