The proposal forms part of a series of plans, which the party says will ease integration for newly-arrived immigrants.
The language test was first proposed by the party ahead of the 2002 election.
Other proposals in the party's new "integration package", presented today, include a demand that any immigrant that wants to bring his or her family to Sweden first has to get a job and find somewhere permanent to live. However, children under the age of 18 will always be allowed to join their parents, the party says.
The party also recommends using temporary residence permits, which will be automatically turned into permanent residency if the immigrant gets a job, or if he or she is still in need of asylum after three years. The Liberal Party also wants to liberalise labour laws in Sweden and speed up the recognition of foreign degrees and training.
The package is to be discussed at a party conference in the Autumn.
Reaction from the Social Democrat-Green Party government has been swift and damning. Top Social Democrat Veronica Palm calls the plans "not just dark-brown, dog-whistle politics, but also ineffective and counterproductive if the aim is indeed better integration".
The Green Party's migration spokesman, Maria Ferm, is also critical: "It is incredibly sad that the Liberals propose temporary residence permits. It splits families, makes integration more difficult, and costs more."