Add bilingual manual and localized docs routes

doc/manual/source/language/expression/function.md

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+# Function Expression
+
+A function expression is a value that accepts arguments and returns an expression.
+
+```dcdl
+(value: Int) => value + 1
+```
+
+See [Functions](../functions.md) for the complete function specification.
+
+## Evaluation
+
+A function can reference bindings from the lexical scope where it was defined.
+Its body is evaluated when the function is called, not when the function value is created.