feat(i18n): implement localisation (#197)

[perzeuss]

This Feature implements:

• Localization for all communications between commando and users.
• A (default) command to get and set the global/guild language and load/reload language files.

To translate commando into your language simply do the following:

1. Create a language file by using the included util createTranslationFile found in src/i18n/dev.js

2. Create a folder for each language and place the language file just created into it

3. Define the translation settings in the CommandoClient#options like:

        new CommandoClient({
            commandPrefix: '!',
            i18n: {
                debug: true, // Enables debug mode of i18next which will tell you if locale files where not found
                loadTranslations: true, // If you set this to false, Commando will not look for translation files and instead load the builtin ones
                localesPath: path.join(__dirname, 'i18n/{{lng}}/{{ns}}.json'), // Define where you've put the translation files. Leave `{{lng}}` and `{{ns}}` as they tell i18next where to look for language files. In this case it will look in `i18n/en/commando.json` to load the language file for `en`
                supportedLanguages: [ 'de', 'fr', 'en'], // Tip: This are the languages you can swith to using the command `!language CODE`
                overrides: {
                // You can configure everything from https://www.i18next.com/overview/configuration-options in here
                },
            },
        });

Learn how to use translations

I've created a guide on repl.it where you have a playground with a working example of commando with translations.

[d-513]

Thank you so much, locale was the only thing that kept me from using Commando for all my bots since some are specifically made for my non-english server. I used a patch workaround but I really do think this PR will be very useful.

[FlyCrafting]

when you plan to merge it? I'm waiting this feature.

[CraftyDragon678]

public language: string; is required

[perzeuss]

when you plan to merge it? I'm waiting this feature.

After a conversation with @Gawdl3y I started to rewrite the code to implement the Loader/Loadable functionality according to the ideas from #196, but I had no time to complete the work.

I've reviewed my changes and pushed what I have so far, but I did not have time yet to test it and there are some changes I want to make.

Since the code isn't ready to merge, I'll close this PR and re open it when I'm done.