Right-to-left support for Twitter Mobile

Friday, 21 December 2012

Thanks to the efforts of our translation volunteers, last week we were able to launch right-to-left language support for our mobile website in Arabic and Farsi. Two interesting challenges came up during development for this feature:

1) We needed to support a timeline that has both right-to-left (RTL) and left-to-right (LTR) tweets. We also needed to make sure that specific parts of each tweet, such as usernames and URLs, are always displayed as LTR.

2) For our touch website, we wanted to flip our UI so that it was truly an RTL experience. But this meant we would need to change a lot of our CSS rules to have reversed values for properties like padding, margins, etc. — both time-consuming and unsustainable for future development. We needed a solution that would let us make changes without having to worry about adding in new CSS rules for RTL every time.

In this post, I detail how we handled these two challenges and offer some general RTL tips and other findings we gleaned during development.

General RTL tips

The basis for supporting RTL lies in the dir element attribute, which can be set to either ltr or rtl. This allows you to set an element’s content direction, so that any text/children nodes would render in the orientation specified. You can see the difference below:

Right-to-left support for Twitter Mobile

In the first row, the text in the LTR column is correct, but in the second it’s the text in the RTL column.

Since this attribute can be used on any element, it can a) be used to change the direction of inline elements, such as links (see “Handling bidirectional tweet content” below) and b) if added to the root html node then the browser will flip the order of all the elements on the page automatically (see “Creating a right-to-left UI” below).

The other way to change content direction lies in the direction and unicode-bidi CSS properties. Just like the dir attribute, the direction property allows you to specify the direction within an element. However, there is one key difference: while direction will affect any block-level elements, for it to affect inline elements the unicode-bidi property must be set to embed or override. Using the dir attribute acts as if both those properties were applied, and is the preferred method as bidi should be considered a document change, not a styling one.

For more on this, see the “W3C directionality specs” section below.

Handling bidirectional tweet content

One of the things we had to think about was how to properly align each tweet depending on the dominant directionality of the content characters. For example, a tweet with mostly RTL characters should be right-aligned and read from right to left. To figure out which chars were RTL, we used this regex:


Then depending on how many chars matched, we could figure out the direction we’d want to apply to the tweet.

However, this would also affect the different entities that are in a tweet’s content. Tweet entities are special parts included in the text that has their own context applied to them, such as usernames and hashtags. Usernames and URLs should always be displayed as LTR, while hashtags may be RTL or LTR depending on what the first character is. To solve this, while parsing out entities we also make sure that the correct direction was applied to the element the entities were contained in.

If you are looking to add RTL support for your site and you have dynamic text with mixed directionality, besides using the dir attribute or direction property, you could also look into the \u200e () and the \u200f () characters. These are invisible control markers that tell the browser how the following text should be displayed. But be careful; conflicts can arise if both the dir / direction and character marker methods are used together. Or if you are using Ruby, Twitter has a great localization gem called TwitterCldr which can take a string and insert these markers appropriately.

Creating a right-to-left UI

For our mobile touch website, we would first detect what language the user’s browser is set in. When it’s one of our supported RTL languages, we add the dir attribute to our page. The browser will then flip the layout of the site so that everything was rendered on the right-hand side first.

This worked fairly well on basic alignment of the page; however, this did not change how all the elements are styled. Properties like padding, margin, text-align, and float will all have the same values, which means that the layout will look just plain wrong in areas where these are applied. This can be the most cumbersome part of adding RTL support to a website, as it usually means adding special rules to your stylesheets to handle this flipped layout.

For our mobile touch website, we are using Google Closure as our stylesheet compiler. This has an extremely convenient flag called —output-orientation, which will go through your stylesheets and adjust the rules according to the value (LTR or RTL) you pass in. By running the stylesheet compilation twice, once with this flag set to RTL, we get two stylesheets that are the mirror images of each other. This fixed nearly all styling issues that came from needing to flip CSS values. In the end, there were only two extra rules that we needed to add to the RTL stylesheet - those were put into rtl.css which gets added on as the last input file for the RTL compilation, thusly overriding any previous rules that were generated.

After that, it’s just a matter of including the right stylesheet for the user’s language and voila! a very nicely RTL’d site with minimal extra effort on the development side.

One last thing that we needed to think about was element manipulation with JS. Since elements will now be pushed as far to the right as possible instead of to the far left, the origin point in which an element starts at may be very different than what you’d expect - possibly even out of the visible area in a container.

For example, we had to change the way that the media strip in our photo gallery moved based on the page’s directionality. Besides coordinates changing, an LTR user would drag starting from the right, then ending to the left in order to see more photos. For an RTL user, the natural inclination would be to start at a left point and drag to the right. This is something that can’t be handled automatically as with our stylesheet compiler, so it comes down to good old-fashioned programming to figure out how we wanted elements to move.

Improving translations

We would like to thank our amazing translations community for helping us get to this point. Without your efforts,we would not have been able to launch this feature onto mobile Twitter. And although we’ve made great strides in supporting RTL, we still have more work to do.

We would love to have more translations for other languages that are not complete yet, such as our other two RTL languages Hebrew and Urdu. Visit translate.twitter.com to see how you can help us add more languages to Twitter.

Helpful Resources

W3C directionality specs:

More resources:

Posted by Christine Tieu (@ctieu)
Engineer, Mobile Web Team