Add bilingual manual and localized docs routes

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+# Introduction
+
+Decodal is the **Deferred Constraint Data Language**, abbreviated **DCDL**.
+Its source files use the `.dcdl` extension.
+
+Decodal is a language for describing configuration values, schemas, constraints, and derived configuration in one expression system, producing validated structured data.
+
+## Purpose
+
+In conventional configuration systems, values, schemas, defaults, derived settings, and validation are often handled by separate mechanisms.
+Decodal treats them as composable expressions.
+
+```dcdl
+Port = Int & >= 1 & <= 65535;
+
+Service = {
+    host = String;
+    port = Port default 8080;
+};
+
+Config = {
+    host = "127.0.0.1";
+    port = 8000;
+} as Service;
+```
+
+`Service` describes a range of accepted values.
+Each value in `Config` is validated against `Service`, while ranges that exist only in `Service` remain abstract in the result.
+During materialization, explicit values take precedence and `default` supplies values for ranges that remain unspecified.
+
+## Core concepts
+
+- Values and constraints are expressions that can be referenced and composed in the same way.
+- `&` performs symmetric composition and preserves constraints from both sides.
+- `as` verifies that the left side is more specific and narrower than the right side, then combines them.
+- `//` performs a right-biased structural patch, including overrides.
+- `default` is not a constraint. It is a fallback selected only during materialization.
+- Object fields, function arguments, and imports are evaluated when they are needed.
+- `Unknown` is the top range that accepts any concrete value, but it cannot be materialized while it remains abstract.
+
+## Scope
+
+Decodal is specialized for describing configuration, schemas, constraints, and derived data.
+General-purpose state mutation, time, randomness, network access, and `try / catch` for treating errors as values are not language features.
+The host provides filesystem and external-format access. Given the same source, import results, and global bindings, Decodal evaluation is deterministic.
+
+Regular-expression constraints depend on the runtime's `regex` feature.
+Decodal does not provide advanced type inference, exhaustiveness checking for `match`, or static detection of unreachable branches.
+
+## Continue reading
+
+- [Language Specification](./language/index.md): syntax, values, expressions, constraints, evaluation, and materialization.
+- [Embedding](./embedding.md): Rust and JavaScript execution, host environments, structured imports, and language services.
+- [Packages and Integrations](./components.md): crates and JavaScript packages for each use case.