This script will take the first command-line arguments and add as many umlauts as possible to it.

gistfile1.py

#!/usr/bin/python
# coding=utf8

import sys

umlauts = {
	'A': [ 'Ä', 'Ǟ' ],
	'a': [ 'ä', 'ǟ' ],
	'E': [ 'Ë' ],
	'e': [ 'ë' ],
	'h': [ 'ḧ' ],
	'H': [ 'Ḧ' ],
	'I': [ 'Ḯ', 'Ḯ' ],
	'i': [ 'ï', 'ḯ' ],
	'O': [ 'Ö', 'Ȫ', 'Ṏ' ],
	'o': [ 'ö', 'ȫ', 'ṏ' ],
	'U': [ 'Ü', 'Ǖ', 'Ǘ', 'Ǚ', 'Ǜ', 'Ṳ', 'Ṻ' ],
	'u': [ 'ü', 'ǖ', 'ǘ', 'ǚ', 'ǜ', 'ṳ', 'ṻ' ],
	'W': [ 'Ẅ' ],
	'w': [ 'ẅ' ],
	'X': [ 'Ẍ' ],
	'x': [ 'ẍ' ],
	'Y': [ 'Ÿ' ],
	'y': [ 'ÿ' ]
}

o = []

for c in sys.argv[1]:
	if c in umlauts:
		o.append(umlauts[c][0])
		if len(umlauts[c]) > 1:
			umlauts[c].pop(0)
	else:
		o.append(c)

print ''.join(o)