Advanced input method options and tools
Use the Microsoft Input Method Editor (IME) to type in East Asian languages you’ve installed on your PC.
Press and hold (or right-click) the input method indicator to switch input modes, then open the IME pad or open more IME settings. For some languages, you'll have more options such as the dictionary tool for Japanese.
Add a word to the Japanese dictionary
Your IME can find more candidates when you turn on cloud suggestion, which uses Bing to help predict what you write. To turn it on, right-click on the input method indicator and select Properties. Then select Advanced and open the Predictive Input tab. Select the checkbox next to Use cloud suggestion.
To add a word to the dictionary manually, go to Start > Settings and select Time & Language. From here, go to Region & Language and select a language, for example, Japanese (日本語). Choose Options. Under Keyboards select Microsoft IME > Options. Now add a new word and its meaning, or edit an existing word by selecting Open Dictionary Tool.