Being somewhat new to Ruby I'm exploring existing libraries to do what I'd normally do in other scripting languages, and I'm a bit stumped by the localization libraries that might be available for something built on top of Sinatra/Sequel (Rails/AR being a bit too opinionated to my taste).
Now, I ran into a couple (i18n, r18n, GetText) though this wiki page, and there apparently is an extra library used in Padrino (based on the i18n thing from Rails?); and apparently plenty more.
Except for the obvious (i.e. GetText mo/po style vs yml files), I'm somewhat confused as to how these options might be different. The wiki doesn't point to much in that respect except saying the that they exist; not how they're different.
Adding to this confusion is the fact that essentially every piece of documentation seems to cover a single one of them (and typically in a RoR context). Moreover, these options don't look entirely incompatible with one another on closer inspection -- in the sense that, if I understood this properly, they can understand each other's files to a large extent.
Might anyone here be able to give a quick and to the point explanation/overview of these libraries, and outline the difference between the them? Some pointers on performance would also be welcome, if you're aware of any (besides the ones from the fast_gettext docs, which made little sense considering my lack of understanding the difference between these options).
I can see how this situation is confusing without knowing some of the history of i18n/l10n libraries in Ruby. I should probably write a few words up on that, but for now I'll try to give an overview from my perspective:
Gettext is obviously the oldest player in this game and it inherits both strengths and weaknesses from its ancestry which is being invented for a C dominated world. It has most features one needs, comes with some tools support that others lack (like desktop po file editors) and is widely accepted in the so called enterprise world.
Gettext as such defines an API and there are basically two libraries that implement it in the Ruby world, the traditional Ruby Gettext packages by Masao Mutoh and the fast_gettext gem by Michael Grosser.
Ruby Gettext is quite powerful and ships a lot of features that you may or may not need. The fast_gettext gem on the other hand focusses on raw speed and is implemented as a shiny, modern code-style Ruby library that is easily hackable and the author is a very smart and supportive person. Out of the two I'd personally strongly recommend fast_gettext.
The I18n gem is the result of the joint effort of various Ruby i18n/l10n solutions that existed a few years ago and that all strived to supersede Gettext for various reasons at that point of time. The resulting I18n API is basically covering the requirements and usecases of all the i18n/l10n solutions involved at that time, including the API of Gettext. So, today's Ruby I18n API is a superset of Gettext's API from the early 90s.
Today the I18n gem is the official solution that is shipped with Ruby on Rails, but it is also the probably most popular one in the Ruby world in general.
The I18n gem also makes it very easy to extend the featureset and add things like caching, other storage mechanisms (like Gettext po files, database tables, key-value stores; storage defaults to plain Ruby files and YAML) etc. and it ships with a number of modules for that (but external or custom modules can easily be crafted, tested and integrated).
There are translation files for 70+ languages (locales) for strings used by Ruby on Rails (which are useful in other projects, too) maintained by the community.
I can not tell much about R18n except that it was invented right after I18n hit its first release and as far as I remember it originated from the Merb community. It seems to be rather strong in the Russian Ruby world, but I might be wrong with all these assertions.
So, unless you have a very good reason to pick any other solution I'd strongly recommend using I18n.
Then on the other hand that means nothing because I've been leading this project more or less since it was invented.
I hope this helps.
[EDIT] added links to various references