This is not just the English form of Thekla - it is also the latinized form of Thekla. As such, the name should be added to either the 'Ancient Greek (Latinized)' category or the 'Greek (Latinized)' category.Also, the 'History' category is (partially) intended for historic names that are no longer or rarely used by people nowadays. That isn't true for this name at all. It has been used in the English-speaking world (so it should be added to the 'English' category). It is also frequently used in The Netherlands, where it is actually more common than Thekla (the original Greek form). In 2010, for Thecla, there were nearly 700 bearers (of all ages) in all of The Netherlands. Whereas for Thekla, the total was nearly 200 bearers in that year. As such, this name also fits in the 'Dutch' category. :) [noted -ed]
Also, the 'History' category is (partially) intended for historic names that are no longer or rarely used by people nowadays. That isn't true for this name at all. It has been used in the English-speaking world (so it should be added to the 'English' category). It is also frequently used in The Netherlands, where it is actually more common than Thekla (the original Greek form). In 2010, for Thecla, there were nearly 700 bearers (of all ages) in all of The Netherlands. Whereas for Thekla, the total was nearly 200 bearers in that year. As such, this name also fits in the 'Dutch' category. :) [noted -ed]