A multilingual Joomla website offers you a greater reach in terms of visitors. The disadvantage is that maintenance takes up more time, especially if the website is not structured efficiently.
How to organize your multilingual Joomla website?
Setting up a new site versus converting an existing website
It is slightly more complicated to convert an existing Joomla website to a multilingual website than to start a new multilingual website. When converting an existing website, you have to manually configure a lot of options. db8 has made a Joomla Multilingual Checklist for this.
System texts versus content
In a multilingual website you deal with a system language and a content language. System Languages ensure that system texts on the front (eg "read more" button) are displayed in the correct language. This can be arranged using language files. Such system texts can be changed via language "overrides".
Content languages ensure that the site can offer managers articles in different languages. Items and menu buttons from one language can be linked to articles and menu buttons from another language. Experience shows that not all content has to be available for all languages. Decide in advance which areas are important for other languages.
LTR versus RTL
Most languages are read from left to right (LTR). Arabic and Hebrew read from right to left (RTL). This has consequences for the structure and the design of the website.
In general, domain names in a certain country extension (eg .nl) are ranked higher by search engines with the same country extension (eg google.nl). By using plugins, it is possible to make the different languages of the multilingual website available with various top level domains (eg domain.nl for Dutch and domain.co.uk for English).
Managing a multilingual website takes more time. In general, every article should be translated into all languages. And there may be more people working on a website, each in their own language area. Another possibility is that languages are used that are not easily readable. db8 can advise you on this regarding a good workflow.