These existing metrics are limited by either requiring external resources or considering only part of the embedding structure (e.g., intra-lingual but not cross-lingual neighbors).
we focus on MUSE  since it is unstable, especially on distant language pairs (Artetxe et al., 2018a;Søgaard et al., 2018;Hoshen and wolf, 2018) and therefore requires an effective metric for model selection.