Add mod documentation in seven languages

docs/en.md

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+# Effects Engine — animated visual effects for scenes
+
+Effects Engine lets a scenario play a short visual effect over a scene: a flash, smoke, sparks, a magic glow. An effect is a small Godot scene that a mod ships in its `effects/` folder; a scenario starts it by name, and it stays on screen until it finishes by itself or the dialog ends.
+
+It is an engine mod with nothing to see on its own. The games currently included do not ship any effect scenes yet, so you will not meet an effect while playing them; this mod is there for authors who want to add one.
+
+## How an effect appears
+
+1. A scenario line `effect <name>` runs.
+2. Effects Engine finds the scene `effects/<name>.tscn` in the loaded mods.
+3. The effect is placed over the scene's picture — above the background and its objects, below the dialog box — and plays.
+4. When the dialog that started it ends, the effect is removed, unless it has already removed itself.
+
+The scenario does not wait for the effect: the next line is shown at once.
+
+## For authors: add an effect
+
+Put the effect's scene in your mod:
+
+```filestree
+my_mod/
+└── effects/
+    └── sparks.tscn
+```
+
+Start it from a scenario:
+
+```scenario
+text "The lamp flickers."
+effect sparks
+text "Something moved in the dark."
+end
+```
+
+**Mods must be folders.** Godot scenes can only be loaded from a mod installed as a folder. A mod distributed as a `.zip` archive has its effects skipped, with a warning in the log.
+
+### Building blocks for the effect scene
+
+Effects Engine provides three ways to animate frames inside your effect scene:
+
+- **Frame set with cross-fade** — a node with the `EffectDataSet` script, a list of frame pictures and an `AnimationController` that fades from one frame to the next. Speed and the fade time are set in the inspector; the frames play once and the effect removes itself.
+- **Sprite sheet in a shader** — `EffectAnimator` steps a `TextureRect` with a frame-sheet material through a set number of frames over a set duration.
+- **Sprite sheet without a shader** — `EffectAnimNode` scrolls through a horizontal sprite sheet (frame width = sheet width / frame count) and removes itself at the end. It can also be created from code with `EffectAnimNode.SpawnOn(target, sheet, frameCount, seconds)`.
+
+The frame set and the code-only sprite sheet stretch to fill the scene, so frames drawn for the scene's size line up with the background.
+
+### A first effect without code
+
+The simplest effect is a scene whose root is a `TextureRect` with a picture, stretched to the full screen — for example a semi-transparent glow. It appears with `effect <name>` and disappears when the dialog ends.
+
+## If something goes wrong
+
+1. **Nothing appears and the log says the effect was not found.** The file must be `effects/<name>.tscn` in a mod that is part of the game, and the name in the scenario must match.
+2. **The effect works in development but not for players.** The mod was published as a `.zip`; publish it as a folder.
+3. **The effect never goes away.** It stays until its dialog ends; end the dialog, or build the effect from the frame-set or sprite-sheet blocks, which remove themselves when they finish.