Ringer,

(1) Your wife ist right, you can replace each 'Umlaut' by the respective vowel folled by 'e'.
(2) In a search, however, the Umlaute are not found when you enter 'ae', 'oe', 'ue'.
(3) "Oh wie schoen ist Panama" finds you the book only if the title has been entered this way. This has been done in some international bookshops.
(4) You can find the book by entering in Google 'ist Panama' and 'Janosch' (the author).

cheers Wolfgang