Language aliased as 'zh-CN' is downloaded as 'zh_CN'

There is a language "zh-Hans-CN" in aliased as "zh-CN" in my project "ovirt-web-ui". When translations are pulled from zanata using zanata-cli, it is downloaded as "zh_CN.po" instead of zh-CN.po" (dash replaced by underscore).

zanata-cli console output correctly mentions the alias with dash, see below.
zanata.xml intentionally doesn't contain "<locale map-from=" mapping since it is discouraged by http://docs.zanata.org/en/release/client/configuration/#locale-configuration.

Console:
$ zanata-cli pull
/usr/bin/build-classpath: Could not find findbugs-annotations Java extension for this JVM
/usr/bin/build-classpath: error: Some specified jars were not found
[INFO] Loading project config from zanata.xml
[INFO] Loading user config from /home/jakub/.config/zanata.ini
[INFO] client API version: 4.2.1, server API version: 3.9.1
[WARN] client API version is 4.2.1, but server API version is 3.9.1
[INFO] Server: https://translate.zanata.org/
[INFO] Project: ovirt-web-ui
[INFO] Version: 1.1.0
[INFO] Username: jniederm
[INFO] Project type: gettext
[INFO] Enable modules: false
[INFO] Using ETag cache: true
[INFO] Purging ETag cache beforehand: false
[INFO] Locales to pull: [ja, it, fr, es, pt-BR, de, zh-Hans-CN(zh-CN), ru, ko]
[INFO] Encode tab as \t: true
[INFO] Current directory: /home/jakub/src/ovirt-web-ui
[INFO] Pulling target documents (translations) only
[INFO] Target-language base directory (translations): extra/from-zanata
[INFO] Minimum accepted translation percentage (message based): 0%
[INFO] Create skeletons for untranslated messages/files: false
[INFO] Pulling 1 of 1 docs for this module from the server
[?] This will overwrite/delete any existing translations in the above directory.

Are you sure (y/n)? y
[INFO] No translations found in locale ja for document messages
[INFO] No translations found in locale it for document messages
[INFO] No changes in translations for locale fr and document messages
[INFO] No translations found in locale es for document messages
[INFO] No translations found in locale pt-BR for document messages
[INFO] No translations found in locale de for document messages
[INFO] No changes in translations for locale zh-Hans-CN and document messages
[INFO] No translations found in locale ru for document messages
[INFO] No translations found in locale ko for document messages

zanata.xml:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<config xmlns="http://zanata.org/namespace/config/">
<url>https://translate.zanata.org/</url>
<project>ovirt-web-ui</project>
<project-version>1.1.0</project-version>
<project-type>gettext</project-type>

<src-dir>extra/to-zanata</src-dir>
<trans-dir>extra/from-zanata</trans-dir>
</config>

server: current translate.zanata.org 3.9.6 (git-server-3.9.6)

$ zanata-cli --version
/usr/bin/build-classpath: Could not find findbugs-annotations Java extension for this JVM
/usr/bin/build-classpath: error: Some specified jars were not found
zanata-cli
Client version: 4.2.1
Client timestamp: unknown
Client SCM describe: unknown
API version: 4.2.1
API timestamp: unknown
API SCM describe: unknown