Support i18n via 'text' functions

[cooperka]

Motivation

Our team needed per-user internationalization, so I went with a quick and easy solution that works for us. If this deserves more thought before being integrated into the official codebase, I'm happy to wait on the PR and help do it "right". Just let me know what you need.

Related issues: #41, #947

Changes

Adds support for text as a function, in addition to the existing string or array options, e.g.

// Simple string:
convo.say('Hello');

// Randomly picks one possibility from the array:
convo.say({ text: ['Hi', 'Hello'] });

// New function-based text:
convo.say({ text: (vars) => vars.isMorning ? 'Good morning' : 'Good evening' });

Example

Code snippets below for a multilingual bot using the polyglot lib for translations (though other libs like i18next would work just as easily).

First set the user's locale on every message via middleware (perhaps you've saved their preference in your database):

function setUserLocale(bot, message, next) {
  const locale = determineUserLocale(message.user);
  bot.getConfig('activity').userDeclaredLocale = locale;
  next();
}

controller.middleware.ingest.use(setUserLocale);

Then save the locale as a conversation variable at the beginning of the conversation:

const convo = new BotkitConversation('myConvo', controller);

convo.before('default', (convo, bot) => {
  convo.setVar('locale', bot.getConfig('activity').userDeclaredLocale);
});

Finally, use whatever method you want to in order to translate each outgoing message:

convo.say({ text: (vars) => i18n[vars.locale].t(text) });

It does indeed work with our fork -- just modify your package.json dependency to:

"botkit": "sassafrastech/botkit#2019-07-28-textFn-v4.5.0-2"

Note: Full docs/testing not yet implemented, since there will probably be some discussion before accepting this PR. Again, I'm happy to make changes to allow wider use of this feature.

[benbrown]

Interesting solution, well documented!

I'll have to ponder this a bit to make sure it doesn't break the world.

[smoyte]

@benbrown Any updates here? Any support we can provide? This is going to be a core part of our use of botkit so if it's going to "break the world" we'll need to know soon :D

I see another person opened a similar PR: #1799

Hopefully we can figure something out...

[benbrown]

I am planning on including this in the next release!

[smoyte]

Wow, great!