Are those text fields with auto-enter calculations, stored calculations or unstored calculations?
Existing data will not update for such an expression as Monthname ( DateFieldHere ) unless it is an unstored calculation or the date in DateField is modified.
You may also have to save a clone of your database on the machine with different locality settings and then import all your data from the original file into the clone before you get all parts of the FileMaker file responding correctly to the change in locality. You also need to check the Text tab in File Options to see if it is set up to use system settings or not.
Thank you Phil,I'll try to scratch..