Your regional settings are derived from the "Account Settings" section of your Microsoft Account. From SkyDrive, you can click your name in the top right, then click Account Settings. Clicking "Edit Personal Info" takes you to a page that lists your
Country/Region.
If you want different regional settings today, you must change this Country/Region setting for your Microsoft account.
For most people in most scenarios, this setting does provide the locale information they expect based on their country or region in which they live. However, there are scenarios such as these where more granular control is desired. In this case all data
is rendered according to your regional settings, and UI/menus are rendered according to your language settings. Formulas happen to be part of the data, and so they are rendering according to your regional settings.
While we can't comment on future features, Microsoft appreciates and is interested in your feedback. Does changing your Country/Region work for you? Do you expect another configuration option to manage your regional settings? Or would more formatting
options in the web app solve your problem?