Wikipedia:Usage of diacritics

For a foreign-language placenames or personal names:
 * 1) When person or place has a native name in the Latin alphabet including letters with diacritics (or some ligatures), e.g. Å, Œ, Ř, Ŵ, names should be spelt with them. (e.g., Ngô Đình Diệm), subject to the exceptions below.
 * 2) Where a name which is clearly the best-established in English differs in spelling, other than merely in terms of diacritics or ligatures, from the native name, then the English name is used.
 * 3) When a name includes Latin "extensions" (and other more obscure ligatures), e.g, Ŋ, ß, Ʌ, Þ, the name should be spelt with the normal Latin substitute for these extensions (e.g., Abülfaz Elçibay, not Əbülfəz Elçibəy)
 * 4) Certain letters with unusual circumstances follow national conventions. For example, Đđ (D with stroke) is rendered "Dj" in South Slavic contexts following usual English conventions but is rendered "Đ" in Vietnamese contexts.  Ðð (eth) is rendered as "Dh" in Icelandic, Faroese contexts due to the complication of the lowercase form, "ð".
 * 5) When a person has changed his or her name (for example, in the process of naturalization as a citizen of another country), the new form of the name is used. So,this rule would apply to the  Edward George de Valera who became Éamon de Valera,  Wilhelm Oberdank who became  Guglielmo Oberdan, Ivan Vučetić who became Juan Vucetich etc.

The above rules apply to mentions of names within articles as well as article titles; alternative names and spellings should be set up as redirects.

Examples
Application of this rule would probably result in Meissen, but Göttingen; Goering but Dvořák; Lech Wałęsa but Stanislaw Ulam and George Frideric Handel; Munich and Tokyo but Zürich.