Inserting foreign characters in text fields

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Hi,
how does one enter characters of a foreign language in a text field?
In particular, I am trying to enter the s with caron on top. In Word I would
type <Ctrl>+<Alt>+^ followed by the s. This does not work however for the
text fields in a form.

Is there a way to define a short cut that would give me this character? I
was thinking of using the KeyDown event, but how could I change the character
that was entered? Is there a better way to do this?

Thanks for any help you can provide.
Regards,
Marcus