Multi languages design can be tricky at times. This is because of the way how natural languages are structured. In some cases, you may have to design to group the languages or separate the design. This are some considerations and impact you may face while developing for multi language support.

Careful of your Layout
A common but annoying issue from multi languages support is the length of text. This can totally screw up your layout design. There will come a stage you may have to css for a specific language due to the long text. Another common occurrence is the font size and type. The type of languages used will impact the selection of font size and types. As a rule of thumb, go for simple layout and standard font type and size.
Default or User Specific Language Locale
Another consideration is to determine if you are going to allow default or user specific languages setting. Majority of application captured user language preference to individual users. However, this may be applicable to secured applications. For public settings, you may consider to use browser language locale or allow a one time setup. These preferences are usually the options you can configure or develop. So, you should select the options that suits best.
Multi languages development will incur additional efforts and considerations to layout and user preferences. It is best to setup multi languages from start. This way, you could determine if your support for multi languages are sufficient.