Japanese contracts normally end something like this:

以上、この契約の締結を証として、本書2通を作成し、甲乙双方が記名押印の上、各1通ずつ保有するものとする。

This can be translated:

In witness whereof, the parties hereto have caused this Agreement to be executed in duplicate, each party retaining one (1) copy thereof respectively.

Variations used in contracts found on the internet include:

IN WITNESS WHEREOF, each of the parties set out below has caused this Agreement to be duly executed by its respective, duly authorized officer as of the date first above written.

IN WITNESS WHEREOF, the parties have entered into this Agreement on the dates set forth below.

IN WITNESS WHEREOF, the parties hereto have duly signed this Agreement as of the day and year first above written.

IN WITNESS WHEREOF, the parties to this Agreement by their duly authorized representatives have executed this Agreement as of the date first above written.

IN WITNESS WHEREOF, each of the undersigned has caused this Agreement to be duly executed and delivered in the location set forth below its signature by its proper and duly authorized officer as of the date hereof.

Contracts written in English tend to include the date in the opening paragraph.
Since we are concerned with translating contracts written in Japanese, which tend to write the date at the end of the contract, more often than not the phrase “as of the date first above written” cannot be used in the closing sentence. It is important to check the Japanese and adjust the phrases appropriately.

Using a seal (はんこ) is a common practice in Asia but not in Europe or America.
(In Hong Kong such seals are referred to as “chops”.)

Over the years many clients have asked me why, when they can see記名押印 in the original, they cannot see an equivalent to sign or seal in the translation.
The word “execute” includes the meaning “sign” thus adding “sign, stamp their seal” is unnecessary.

The following is an example of a closing sentence that can be used if requested to include "sign" in the translation:
In witness whereof, the parties hereto have caused this Agreement to be executed by their representatives in duplicate, by affixing their signatures and/or [registered] seals, and each party shall retain one (1) copy thereof respectively.

(Updated from an published by Orian in August 2012)

When writing prose it is common to write single digit numbers, i.e. one to nine out in full and to write numbers larger than 10 in numerals. The same is true with contracts, although it is not unusual to see numbers larger than 10 written out in full too.
In contracts, numbers are usually followed by their numerical equivalent in parentheses.
There is no legal requirement for this practice, however it ensures that confusion, misreading, and misunderstandings are avoided.

In English speaking countries it is common to use a comma in larger numbers (e.g. 10,000).

 However, you may wish to note this:

“In Continental Europe the opposite is true, periods are used to separate large numbers and the comma is used for decimals. Finally, the International Systems of Units (SI) recommends that a space should be used to separate groups of three digits, and both the comma and the period should be used only to denote decimals”

Taken from: http://www.dailywritingtips.com/10-rules-for-writing-numbers-and-numerals/

This means that in some countries “10 000 or 10.000” might be more widely used, so if looks like one of the parties involved might be located in a non-English speaking country, then writing numbers out in full with serve as a way of avoiding misunderstandings.

Be sure to use half-width characters for the yen sign.
If the file corrupts on your clients computer and the character becomes garbled (often as a “\”).
When in doubt use “yen” or “JPY”: 10,000 yen or 10,000 JPY.

Monetary amounts are sometimes written out in full too: “one million one hundred thousand yen (￥1,100,000)”.　However, with the Japanese monetary system, numbers get large very quickly and writing “three million six hundred thousand yen (3,600,000 JPY)” can slow the reader down.

Percentages are also sometimes written out in full too: eighty-five percent (85%)

Whether you decide to write numbers larger than 10 out in full is ultimately your decision, and once you have made your decision be sure to be consistent, especially throughout the same document!

(Updated from an article published by Orian in August 2012)

First the translator (or their client) needs to decide how to handle 甲, 乙, and 丙, etc.

While often used in boilerplates, “Party A” and “Party B” should be avoided wherever possible.
In a long contract it can often be difficult to remember which party is A and which is B so if the name of the parties involved are known, then these should be your first choice.

Depending on the type of contract, Lessor – Lessee, Licensor – Licensee, Buyer – Seller, Company – Employee, etc. are also acceptable.

Only when the name of the party or their status in the contract is unknown and there is no other option available should you resort to Company A – Company B or First Party – Second Party.

I’ve noticed that some translators use block capitals letters for company names or the status of the parties involved.

This is not standard practice in English language contracts, is unnecessary, and should be avoided. Since the parties are defined terms however, using capitals for “Lender”, etc. is standard practice.

(Updated from an article published by Orian in August 2012)