When you visit https://en.wikipedia.org/api/rest_v1/data/recommendation/article/creation/morelike/Book you'll see something like this:
```lang=json
[{"wikidata_id":"Q998687","normalized_rank":0.0000016773},{"wikidata_id":"Q1306010","normalized_rank":0.0000016773},{"wikidata_id":"Q997969","normalized_rank":0.0000016773},{"wikidata_id":"Q998851","normalized_rank":0.0000016773},{"wikidata_id":"Q1489555","normalized_rank":0.0000016773},{"wikidata_id":"Q1811594","normalized_rank":0.0000016773},{"wikidata_id":"Q998758","normalized_rank":0.0000016773},{"wikidata_id":"Q1648227","normalized_rank":0.0000016773},{"wikidata_id":"Q1811586","normalized_rank":0.0000016773},{"wikidata_id":"Q1238507","normalized_rank":0.0000016773}]
```
It would be useful to output source language for each recommended item. Along with the `wikidata_id` and `normalized_rank` properties, output a `source_language` property whose value is the language code for that item, e.g. 'es' for Spanish.