Teutonic Mythology
transl. by Rasmus B Andersen. London & New York 1889.
Covers vol. I of Undersökningarna only. Reissued by Norroena Society 1906 in three de luxe volumes , with the subtitle gods and goddesses of the Northland. Available in several editions on the book market (see amazon.com).
Free e-versions:
(London, 1889): Internet archive
(1906 edition): vol 1; vol 2; vol 3; (Internet archive)

Victor Rydberg's Investigations into Germanic mythology, vol.2, part 1-2
transl. by William P. Reaves. New York: iUniverse, 2004-2007.
Covers the second volume of Undersökningar i germanisk mythologi.