Norwegian first names

I frequently find my searches more difficult because I do not understand or appreciate the different spellings and form of first names. The common names (or nick-names) compound the problem. This is increasingly difficult when trying to identify people that have migrated to a new country with many different languages, alphabets, accents and spellings. The traditional handwriting practices compound the problem. A prime example is an 1800's U.S. census where a Norwegian is answering a census questions posed by a first generation German that is required to make an entry in English (American?) that will be recorded and published. I found a "family " name of Ondell that was somehow trandlated into Ollendorf. Are ther any source that may give a curious person some ideas of spelling variations and "nick names" or common names as a first name. Family names are diffferent problem that relate to the unique root language. Another problem is that the first/given name may be altered or abandoned during immigration. This is a universal problem for anyone doing genealogy and trying to "bridge" the gap that occurred during migration to a new country with radically different languages, accents and habits. Are there any sources to minimize the challenge? Thanx (American term) for any help!! Dick