This:
root@scb1001:~# tail -1 /srv/log/mobileapps/main.log
{"name":"mobileapps","hostname":"scb1001","pid":2053,"level":50,"message":"501: unsupported_language","stack":"HTTPError: 501: unsupported_language\n at parse (/srv/deployment/mobileapps/deploy/src/lib/parseDefinition.js:198:15)\n at Request.<anonymous> (/srv/deployment/mobileapps/deploy/src/lib/parsoid-access.js:166:20)\n at Request.tryCatcher (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/util.js:24:31)\n at Promise._settlePromiseFromHandler (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/promise.js:582:31)\n at Promise._settlePromiseAt (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/promise.js:727:18)\n at Promise._settlePromises (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/promise.js:845:14)\n at Async._drainQueue (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/async.js:79:16)\n at Async._drainQueues (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/async.js:89:10)\n at Async.drainQueues (/srv/deployment/mobileapps/deploy/node_modules/bluebird/js/main/async.js:14:14)\n at doNTCallback0 (node.js:419:9)\n at process._tickCallback (node.js:348:13)","status":501,"type":"unsupported_language","detail":"The language you have requested is not yet supported.","levelPath":"error/501","request_id":"2c3fcb4e-be9e-11e5-bf64-261415c16aec","msg":"501: unsupported_language","time":"2016-01-19T11:17:06.557Z","v":0}is being spamming the logs quite a bit:
root@scb1001:~# grep -c unsupported_language /srv/log/mobileapps/main.log 13002 root@scb1001:~# head -1 /srv/log/mobileapps/main.log | jq .time "2016-01-19T06:25:23.369Z" root@scb1001:~# date Tue Jan 19 11:19:51 UTC 2016
I have no idea if it's a real user-facing error or not, but in any case it's quite distracting.
Also, an error code in the 5xx range is probably not the right one for such an issue — this sounds like something that could fit in the 4xx range, possibly even a 404.