There is a relatively extensive organized language management in Czech, focused on spelling that goes back to the national movement. Due to the rich inflectional system in Czech, all loanwords tend to be integrated into one of the declension paradigms.
Accepting loanwords is thus a long process, which can be traced in a gradual adaptation of their transcription to the Czech spelling. Most of the loanwords from Icelandic and Old Norse have already "found their declensions" and are transcribed as they are pronounced in Czech.
In the Czech translations of modern Icelandic literature, we can probably say that some kind of consensus is slowly forming. The nom. ending of masculine names is mostly omitted in oblique cases.
But in contrast to Old Norse names, it has been shown that in nom. masc. the ending is mostly retained for Icelandic names.