Hi! We have a website (apptamin.com). We're starting to target the Chinese market and therefore decided to do a localized website (apptamin.cn - not live yet) in Chinese. It will be localized in terms of content, but also optimized for Baidu SEO. We are using WPEngine, and I created a new install there with the same content that we plan to put on their Linode servers in Japan (what seems to be recommended). I'm just a bit worried that this new install with basically the same content (although it's in Chinese) could harm our existing website and its rankings? Can anyone confirm (or not) that using rel="alternate" hreflang="x" the should be enough (https://support.google.com/webmasters/answer/189077?hl=en)? No need to use canonical?
There is absolutely no duplicate content issue between languages. Even if you can do a word-for-word translation, which is pretty difficult if you want the translation to read appropriately, the search engines are not translating and comparing the content between the sites. They will only look for duplicate content within the same language.
The hreflang is just used to help the search engines know which language you are using, which is important as well.
You'll want to also make sure to translate your image alt tags, and only Google uses rel=canonical, so you might be better off using the “content-language” meta tag for all of the other engines you're targeting. Baidu and Bing use the meta tag instead.
The resource at https://sites.google.com/site/webmasterhelpforum/en/faq-internationalisation#q20 clarifies that if you implement hreflang on your site then you shouldn't implement canonicals tags as well in the same code.
Always make sure you reference the page your code is placed on as well in your hreflang set up as this is sometimes missed by people.
Yoast's plugin in WP is great for in-page hreflang coding implementation. If you are using non WP though then you may want to consider a hreflang .xml sitemap instead. There are not many tools that auto generate an .xml version though. The only one I've found is at https://www.xml-sitemaps.com/standalone-google-sitemap-generator.html. Although Screaming frog told me yesterday that it's on their development roadmap to be integrated into their software, which should be very helpful.
If you are entering into the Chinese market I would also recommend you check out http://www.dragonmetrics.com/ which is very good for monitoring organic performance of your site and helping with keyword research, you can get a free 30 day trial without entering any financial details such as a credit card, so worth setting up once your site is either more established or if you are going through the content optimisation process for the new site.