Icelandic and Swedish are both languages that descend from Old Norse, a language spoken in Scandinavia during the time of the Vikings.
Icelandic has remained closer to the original Old Norse language, whereas Swedish has changed more over time.
The reason for this is the geographical isolation of Iceland, which for centuries has limited the influence of other languages on Icelandic.
Because Icelandic and Swedish descend from Old Norse, these languages share many similar vocabulary words.
Here are some examples of words that are similar in Swedish and Icelandic (and significantly different from their English equivalents):
Because Swedish and Icelandic are different languages, some words are very different between these two languages. Here are some examples of such terms:
For centuries, the geographical isolation of Iceland has sheltered Icelandic from the influence of other languages.
In today's era of global media and the internet, linguistic influence is no longer limited by geographical isolation as it was in the past. Despite this, Icelanders have adopted an active policy of limiting the inclusion of foreign loanwords into their language.
Icelanders prefer creating new words instead of incorporating loanwords into Icelandic. For instance, they coined the word “tölvupóstur” for “email” and “sími” for “telephone”.
Swedish, on the other hand, has been in close contact with other languages for centuries. For instance, during the middle ages, some Swedish cities participated in the Hanseatic League, a trading union that had Middle Low German as its trade language.
As a result, some Swedish vocabulary words are loanwords from German. (see this comparison of German and Swedish for examples)
In many languages, nouns have a grammatical gender. This is particularly common among European languages.
In Icelandic, each noun has one of 3 possible genders (masculine, feminine, or neuter). Swedish is simpler in this regard, with Swedish nouns having one of 2 possible genders (common and neuter).
Icelandic nouns are declined according to 4 grammatical cases (nominative, accusative, dative, and genitive). This means that the ending of the noun changes depending on its grammatical function in a sentence.
Just as noun case declensions (which were present in Old English) disappeared from modern English, these were also present in Old Swedish and disappeared from modern Swedish.
Basically, Icelandic being a more conservative language than other Germanic languages like Swedish and English, has conserved certain grammatical features which have disappeared from these other languages.
In contrast to Icelandic, Swedish verbs do not conjugate according to number and person. In Swedish, the same verb form is used for all subject pronouns.
For example, here is the verb "to be" and its conjugation tables in Swedish and Icelandic:
In Icelandic and in Swedish, the infinitive form of most verbs ends in -a. Examples of common Swedish verbs can be seen in this list of the 1000 most common Swedish words.
In Icelandic and in Swedish, the definite article (which corresponds to the English word “the”) is usually a suffix added to the noun, rather than a word placed in front of it. This is a fairly common feature among Scandinavian languages.
Indefinite articles (which correspond to the English words “a” and “an”) exist in Swedish, but not in Icelandic.
The significant difference in learning difficulty between Swedish and Icelandic is apparent in how these languages are rated by the US Foreign Service Institute (FSI).
Based on their experience in teaching languages to US diplomats, the FSI ranks languages in 4 categories according to their learning difficulty.
Swedish is classified in category I —the easiest category— alongside other accessible languages such as Spanish and Italian.
Icelandic, on the other hand, is classified in category III, alongside some notoriously difficult languages such as Hungarian and Finnish.
Learning Swedish makes these other two Nordic languages (Norwegian and Danish) accessible.
On the other hand, because Icelandic is so similar to Old Norse, knowing Icelandic can enable one to read Old Norse literature, such as the famous Sagas.
Another factor to take into consideration when choosing between learning Swedish or Icelandic is that there are approximately 30 times more native Swedish speakers than there are native Icelandic speakers (10 million vs 300 thousand).
Because Icelandic is significantly more difficult than Swedish, in particular with regards to grammar, language learners who do not enjoy grammar may prefer learning Swedish rather than Icelandic.