Language skills mostly act to limit your use of social skills. When using any skill where your command of the language you are using is a factor (most notably Persuade and Performance, but others may apply), if the language skill has a lower rating than the skill you are rolling, you use that instead.
Example: Alice has Persuade d10, English d12, and Sprawlspeak d8. When trying to Persuade someone using English, she rolls d10. But when using Sprawlspeak, she can only roll d8.
Occasionally, you may also need to roll the language skill itself, eg. to understand something or make yourself understood when acting under time pressure.
In core SWADE, a language is treated as a full skill, costing one skill point per die type to raise. This gets very expensive in settings with lots of languages, so I am replacing it with the following houserules:
At chargen, everyone gets:
Per RAW, the Linguist Edge is “character gains a d6 in a number of languages equal to half her Smarts die.”
As in RAW, the Linguist edge will give you knowledge of a number of languages equal to half your Smarts die. Rather than working at a d6 level, however, in these rules this edge grants Partial level knowledge to the bonus language skills.
These languages can be upgraded to Fluent for one further skill point each.
In my campaign, the Seattle sprawl is a melting pot of Pacific Rim and Native American cultures, and, accordingly, of languages. English, Japanese, Spanish, Korean, Cantonese, Salish, Sioux, Russian; all are commonly heard around the city.
Each megacorp and major criminal organisation typically conducts day-to-day activities in their native tongue:
Two ancient languages have returned to the world with the Awakening:
With a sharp need for inter-group communications across language barriers, a pidgin language has emerged in Seattle and other similar international metroplexes. Called Sprawlspeak or Streetspeak, it is a mixture of half a dozen common languages in the area. Sprawlspeak is a common language amongst ordinary people in lower-class areas; anywhere people from different language groups have to mix and communicate, sprawlspeak flourishes.
In Seattle, the local dialect of sprawlspeak is about half English, with the other half comprised mostly of Japanese, Salish, Sioux, and Cantonese. Loan words from another dozen languages creep in here and there, though.
Over time, linguistic scholars are watching with interest to see if sprawlspeak continues to develop and become a creole.
Sprawlspeak is still an awkward, halting language, although it is becoming more sophisticated and fluid over time. It can only ever be learned to Partial level. There is no such thing as Fluency in sprawlspeak. Therefore, characters planning a social manipulator role would be well-advised to consider taking multiple language skills, so they can converse with their targets in their native tongue.