It is advisable to get what is generally called a "native check" to make sure the translation is accurate, consistent and does not contain phrases with ambiguous or profane words or phrases. However, there are many ways to do this without paying a professional to look at a few lines. This section outlines some of them:
1. Put out a test run of the sign for a few weeks, and ask appropriate customers for their opinions. There are many examples of "amended" signage using this method. For example, a sign at Nasu ropeway started out as this;
Fig. X. Nasu ropeway original sign
but after a short time, was amended to this:
Fig. X Nasu ropeway revised sign
This was certainly due to some friendly input from an English speaking customer or two!
2. Use an online language exchange website or application such as hellotalk or lang-8. To do this, you will have to sign up and "make friends" but it will be easy to explain your sign and have someone help you. You can use simple Japanese or English to ask about signage in other languages. Native speakers who wish to practice English or Japanese will be happy to help you. Here are just a few recommended sites:
(PC) Lang8 http://lang-8.com/ https://mylanguageexchange.com/default_jpn.asp https://coeffee.com/login
(iPhone/android) tandem.net (iPhone only?) https://hellotalk.com/ (iPhone, android) https://www.italki.com/home