Including papers in languages other than English in systematic reviews: important, feasible, yet often omitted.

A truly international and systematic review (SR) identifies and synthesizes relevant evidence regardless of the geographical provenance or language of publication. Despite recommendations, international SRs continue to exclude papers in languages other than English (LOE) at searching, screening, and analysis phases either explicitly in their protocols or by omitting to attend to LOE. Although guidelines on including LOE publications in SRs are lacking, a small body of literature provides strategies for screening LOE titles and abstracts. Drawing on experience from published SRs, this commentary summarizes the existing literature and highlights further strategies that can be used. Online translation tools and language skills of colleagues can often be used during searching and screening at no financial cost. When LOE papers meet inclusion criteria, a member of the SR team with relevant language skills, if available, or an external translator will ideally be involved multiple times during the review process. Weighing up the novelty and import of insights from a paper against translation costs can inform decisions about whether LOE papers should be included and the frequency with which a translator should be involved. Removing language restrictions requires attention at all stages of an SR. A plan for addressing LOE papers at each stage should be documented at the outset of the review and may need to be revised depending on the number of papers identified. Reporting of the approach used is important for transparency and confirmability.