In commenting on a recent blog entry, Kevin Brennan gave an example of a requirement:
"the user interface will be available in English, French, and Spanish"
Kevin's point was to illustrate how some requirements are testable but not quantifiable, since "quantifiable" implies numeric measurement. I understand and agree with his point. "English", "French", and "Spanish" are not numbers :-)
However, I wanted to digress a bit and further evaluate his example of a requirement. His example strikes me more as a design decision than a requirement.
Why would a stakeholder want the user interface to be available in any of those languages? What problem does it solve to make the user interface available in those languages? The problem it solves is making sure that the target market is able to use the product. Presumably, the target market includes a substantial number of English-, French-, and Spanish-speaking people.
The real requirement is to make the product usable by these people. Usability requirements typically include profiles of various types of users. Instead of specifying that the user interface must be available in various languages, the requirements should simply include language-speaking characteristics in the user profiles. The product must satisfy the usability requirements for these users.