x/text/message: better documentation for catalog

[belimawr]

The documentation for this package could be clearer with regard to how catalogs should be used.
Specifically:

• the default catalog is empty.
• how to populate the default catalog (is there a standard way of doing this?)
• document that the default fallback language is English.

Repo commit: b0f49b06765e38644f97dff880167326a7ab0391

[belimawr]

I'm already working on this documentation improvement.

[belimawr]

There is a bit of the discussion on #26766

After more reading of the documentation/code on the package and also the point raised by @kaskavalci, I believe that the best way of making this package example work is to pass the language directly to message.NewPrinter.

[gopherbot]

Change https://golang.org/cl/127598 mentions this issue: message: improve documentation

[kaskavalci]

I think MatchLanguage behavior and its interaction with Catalog is also worth noting. A short example with adding number of languages to Catalog then calling MatchLanguage as in the catalog_test.go could be helpful. Using pre-configured language is straightforward but matching a language on the fly is more interesting use-case.

[belimawr]

@kaskavalci I totally agree with you. I'm planning to extend the http example there to:

• Add a few expressions on the catalog
• Get the language using a request parameter and MatchLanguage
• Return the translated text (not number formatting) on the response.

This way it will be more clear of how all those functions interact with each other.

I hope to get it done by the end of this week.

[beono]

@belimawr Hey buddy :)
I don't know your use case, but this package looks unreliable.
Recently I faced a major issue that had been in the master for 6 months.
https://go-review.googlesource.com/c/text/+/128795

Take a look at this repo https://github.com/nicksnyder/go-i18n

[belimawr]

Hey @beono !

Actually my use case is to contribute with the Golang project. So far I haven't used this package in production yet.

[belimawr]

@kaskavalci I finally had time to update the examples \0/

[kaskavalci]

Thanks @belimawr !

[kaskavalci]

Hey @belimawr

I'm working with message again and hit another problem. This is not from catalog documentation but from message. https://godoc.org/golang.org/x/text/message#example-Printer--MVerb

When you run the example it complains about %m type:

nl     U heeft ervoor gekozen om %!m(string=soccer) te spelen.

Changing it to string type %s resulted in no translation. See soccer is not converted into "voetbal".

nl     U heeft ervoor gekozen om soccer te spelen.

Another weird issue I noticed is in printer. See the following example. Is that the expected behavior?

	message.SetString(language.Dutch, "soccer", "voetbal")
	p := message.NewPrinter(language.Make("nl"))
	p.Printf("soccer\n")             // prints soccer
	fmt.Println(p.Sprint("soccer"))  // prints soccer
	fmt.Println(p.Sprintf("soccer")) // prints voetball

[kaskavalci]

Noticed one more problem. Dutch decimal separator is comma. When NewPrinter is called by MatchLanguage it prints wrong output but with language.Dutch it works as it should.

p := message.NewPrinter(message.MatchLanguage("nl"))
p.Printf("Hoogte: %.1f meter\n", 1244.9) // Prints Hoogte: 1,244.9 meter

m := message.NewPrinter(language.Dutch)
m.Printf("Hoogte: %.1f meter\n", 1244.9) // Prints Hoogte: 1.244,9 meter