Mio C520 - Manual (Page 21)

Number/symbol Keypad
When you tap to enable umlaut, you can tap a vowel letter repeatedly to
input a different form of the letter. Alternatively, you can tap the letter in the
pop-up window as shown below.
Switch to the alphabet keypad.
Umlaut enabled. Tap the
button again to disable it.
After you complete an input, tap .
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