Seldom the barriers between the races seem less in evidence than on this language leading team

Explanation

This is the error. The original sentence lacks subject-verb inversion required for a proper construction. In formal English, when starting a sentence with an adverbial phrase like "Seldom," the subject and the auxiliary verb are inverted. In normal conversation auxiliary verb are used after subject (He seldom does/subject + seldom + auxiliary verb) but when adverbial phrase comes in start of sentence auxiliary verb comes before the subject (Seldom does he/ Seldom + Auxilliary verb + Subject). The corrected version starts with "Seldom do," where "do" is the auxiliary verb. OR you can simply bring "the barriers between the races" before the adverb "seldom" as: The barriers between the races seldom seem less evident than on this language-leading team.So, the corrected sentence is: "Seldom do the barriers between the races seem less in evidence than on this language-leading team."