The original text apparently had a few instances of the base verb form for the subject pronoun thou, as here in Mosiah 26:11 (“that thou may judge them according to their crimes”). In this particular instance, the 1837 edition replaced the base form may with the indicative form mayest. Interestingly, the 1852 edition, set in Liverpool, England, replaced the two-syllable mayest with the dialectal one-syllable mayst, which was retained in the LDS text until the 1920 edition. Elsewhere, the Book of Mormon text has mayest (eight times), but never mayst. And here in Mosiah 26:11, we have the only occurrence of “thou may”. Although this subjunctive usage here may be an error, it is also possible that it is intended, as discussed under Mosiah 12:11. A similar use of the base form of a modal verb also occurs nearby in Mosiah 26:20 (“and thou shalt serve me and go forth in my name and shall gather together my sheep”). For discussion, see that passage.
Summary: Restore in Mosiah 26:11 the original base form may for the modal auxiliary; such usage, although fairly infrequent in the original text, may have been intended here.