Antiquariana: Old Sioux

...owing to the paucity of the old Lakota vocabulary, it is often necessary to express widely varying concepts by the same word or phrase, the comprehension of the concept depending on the association of correct ideas with the expression. The phrases were conventional, but not fixed, for they could be modified by the addition, subtraction, or interjection of words. When the white people heard these phrases they assumed that they were words and wrote them as such. In translating English into Lakota, there was often no Lakota word  equivalent to the English word and in such cases a Lakota word was used to express a concept that was foreign to it. Thus, in written Lakota, the phrases became fixed as words and insusceptible to modification so that many words were given new meanings. Thus was brought about a marked transition of the language, both in structure and meaning, so that there are now both old and modern forms of speech.

—J.R. Walker, The Sun Dance and Other Ceremonies of the Oglala Division of the Teton Dakota, 1917