Principal English Translation: 

between, among, in the midst of (see Lockhart and Karttunen)

Frances Karttunen: 

-TZĀLAN. (postposition). between, among / entre algunos, o por medio dellos (M) This is abundantly attested in C with the vowel of the first syllable long and that of the second syllable never marked long. T has long vowels in both syllables, but the final N is missing. Z has both vowels long. See TZĀLAN-TLI.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 310.

Lockhart’s Nahuatl as Written: 

relational word. between, among, in the midst of. tepētl ītzālan, a valley, a place between mountains. possibly the second a of
-tzālan is long too.
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 240.

Attestations from sources in English: 

tzalan (postpositive) = among, amid
Daniel Garrison Brinton, Ancient Nahuatl Poetry: Containing the Nahuatl Text of XXVII Ancient Mexican Poems (1877), 167.

caltzalan = in the middle of the houses
totzalan = among us, between us