One of the core projects we did over 2017 was a major overhaul of the Localization and Internationalization layers in Gecko, and all throughout the first half of 2018 we were introducing Fluent into Firefox.

All of that work was “behind the scenes” and laid the foundation to enable us to bring higher level improvements in the future.

Today, I’m happy to announce that the first of those high-level features has just landed in Firefox Nightly!

Pseudolocalization?

Pseudolocalization is a technology allowing for testing the localizability of software UI. It allows developers to check how the UI they are working on will look like when translated, without having to wait for translations to become available.

It shortens the Test-Driven Development cycle and lowers the burden of creating localizable UI.

Here’s a demo of how it works:

How to turn it on?

At the moment, we don’t have any UI for this feature. You need to create a new preference called intl.l10n.pseudo and set its value to accented for a left-to-right, ~30% longer strategy, or bidi for a right-to-left strategy. (more documentation).

If you test the bidi strategy you also will likely want to switch another preference – intl.uidirection – to 1 . This is because right now the directionality of text and layout are not connected. We will improve that in the future.

We’ll be looking into ways to expose this functionality in the UI, and if you have any ideas or suggestions for what you’d like to see, let’s talk!

Nitty-gritty details

Although the feature may seem simple to add, and the actual patch that adds it was less than 100 lines long, it took many years of prototyping and years of development to build the foundation layers to allow for it.

Many of the design principles of Project Fluent combined with the vision shaped by the L10n Drivers Team at Mozilla allowed for dynamic runtime locale switching and declarative UI localization bindings.

Thanks to all of that work, we don’t have to require special builds or increase the bundle size for this feature to work. It comes practically for free and we can extend and fine tune pseudolocalization strategies on fly.

Kudos

If that feature looks cool, in the esoteric way localization and internationalization can, please, make sure to high-five the people who put a lot of work to get this done: Staś Małolepszy, Axel Hecht, Francesco Lodolo, Jeff Beatty and Dave Townsend.

More features are coming! Stay tuned.