Hopefully I don't ruffle too many feathers but I don't feel many of these comments, and many of the other thread posted above, are what would be considered professional... As a business person I am not interested in pettiness and bravado in the business realm. Save it for your mates. I often put my personal viewpoints aside and focus on what improves the experience of my customers and my business bottom line. In the big picture that is what counts.
The many variants of the English language are widely recognized. Accommodating these variants is no different than providing lang files for any other language. Most companies if they are wise customize their marketing materials to suit the local market. Language grammar and spelling is a big part of that process. Not everyone is knowledgeable of differences in the English Language and they may view these differences as a spelling error and view the company negatively.
Being Canadian I have become very aware and very tolerant of the mix of UK and US English, thrown together with a far smattering of Canadian French words and sayings, that we experience everyday. But in my business I recognize that the huge US market is my main customer base and they are typically not so aware and tolerant of these differences. I gladly accommodate and cater to them. My Canadian customers on the other hand are so familiar with the variants that it is a non-issue for them. When it comes to business the customer trumps personal biases every time.
I too agree with osCommerce that an English US lang file would be a benefit for many. It would be easy to delete it from the install like all the other lang files that are not needed. Claiming that WHMCS is a British company and so the English lang file will be “British” English is very limiting to the growth of WHMCS.
PS.
Sorry for the rant but language issues are a sore point for me...