Add the translated description: (DATETIME constant)

The translation is based on the contents of https://github.com/php/doc-ja/blob/b2779c2b6e82b116b049f0435dee73dec45b9862/reference/datetime/datetimeinterface.xml

Author: o0h

reference/datetime/constants.xml

@@ -56,7 +56,7 @@
    <term><constant>DATE_ATOM</constant></term>
    <listitem>
     <simpara>
-     Atom (example: <literal>2005-08-15T15:52:01+00:00</literal>)
+     Atom (例: <literal>2005-08-15T15:52:01+00:00</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -65,7 +65,7 @@
    <term><constant>DATE_COOKIE</constant></term>
    <listitem>
     <simpara>
-     HTTP Cookies (example: <literal>Monday, 15-Aug-2005 15:52:01 UTC</literal>)
+     HTTP Cookies (例: <literal>Monday, 15-Aug-2005 15:52:01 UTC</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -74,15 +74,16 @@
    <term><constant>DATE_ISO8601</constant></term>
    <listitem>
     <simpara>
-     ISO-8601 (example: <literal>2005-08-15T15:52:01+0000</literal>)
+     ISO-8601 (例: <literal>2005-08-15T15:52:01+0000</literal>)
     </simpara>
     <note>
      <simpara>
-      This format is not compatible with ISO-8601, but is left this way for
-      backward compatibility reasons. Use
+      このフォーマットは、ISO-8601 と互換性がありません。
+      しかし、後方互換性を保つために残されています。
+      ISO-8601 と互換性を保つためには、
       <constant>DATE_ISO8601_EXPANDED</constant>,
-      <constant>DATE_ATOM</constant> for compatibility with ISO-8601
-      instead. (ref ISO8601:2004 section 4.3.3 clause d)
+      <constant>DATE_ATOM</constant> を使うようにしてください。
+      (ISO8601:2004 section 4.3.3 clause d も参照ください)
      </simpara>
     </note>
    </listitem>
@@ -92,14 +93,14 @@
    <term><constant>DATE_ISO8601_EXPANDED</constant></term>
    <listitem>
     <simpara>
-     ISO-8601 Expanded (example: <literal>+10191-07-26T08:59:52+01:00</literal>)
+     ISO-8601 拡張形式 (例: <literal>+10191-07-26T08:59:52+01:00</literal>)
     </simpara>
     <note>
      <simpara>
-      This format allows for year ranges outside of ISO-8601's normal range
-      of <literal>0000</literal>-<literal>9999</literal> by always
-      including a sign character. It also addresses that that timezone part
-      (<literal>+01:00</literal>) is compatible with ISO-8601.
+      年に常に符号を含めることで、ISO-8601 の通常の範囲
+      <literal>0000</literal>-<literal>9999</literal> 以外の値が許されています。
+      タイムゾーンの部分 (<literal>+01:00</literal>) については、
+      ISO-8601 と互換性をとるようにもなっています。
      </simpara>
     </note>
    </listitem>
@@ -109,7 +110,7 @@
    <term><constant>DATE_RFC822</constant></term>
    <listitem>
     <simpara>
-     RFC 822 (example: <literal>Mon, 15 Aug 05 15:52:01 +0000</literal>)
+     RFC 822 (例: <literal>Mon, 15 Aug 05 15:52:01 +0000</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -118,7 +119,7 @@
    <term><constant>DATE_RFC850</constant></term>
    <listitem>
     <simpara>
-     RFC 850 (example: <literal>Monday, 15-Aug-05 15:52:01 UTC</literal>)
+     RFC 850 (例: <literal>Monday, 15-Aug-05 15:52:01 UTC</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -127,7 +128,7 @@
    <term><constant>DATE_RFC1036</constant></term>
    <listitem>
     <simpara>
-     RFC 1036 (example: <literal>Mon, 15 Aug 05 15:52:01 +0000</literal>)
+     RFC 1036 (例: <literal>Mon, 15 Aug 05 15:52:01 +0000</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -136,7 +137,7 @@
    <term><constant>DATE_RFC1123</constant></term>
    <listitem>
     <simpara>
-     RFC 1123 (example: <literal>Mon, 15 Aug 2005 15:52:01 +0000</literal>)
+     RFC 1123 (例: <literal>Mon, 15 Aug 2005 15:52:01 +0000</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -146,7 +147,7 @@
     <listitem>
      <simpara>
       RFC 7231 (as of PHP 7.0.19 and 7.1.5)
-      (example: <literal>Sat, 30 Apr 2016 17:52:13 GMT</literal>)
+      (例: <literal>Sat, 30 Apr 2016 17:52:13 GMT</literal>)
      </simpara>
     </listitem>
   </varlistentry>
@@ -155,7 +156,7 @@
    <term><constant>DATE_RFC2822</constant></term>
    <listitem>
     <simpara>
-     RFC 2822 (example: <literal>Mon, 15 Aug 2005 15:52:01 +0000</literal>)
+     RFC 2822 (例: <literal>Mon, 15 Aug 2005 15:52:01 +0000</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -164,7 +165,7 @@
    <term><constant>DATE_RFC3339</constant></term>
    <listitem>
     <simpara>
-     Same as <constant>DATE_ATOM</constant>.
+     <constant>DATE_ATOM</constant> と同じです
     </simpara>
    </listitem>
   </varlistentry>
@@ -173,8 +174,8 @@
    <term><constant>DATE_RFC3339_EXTENDED</constant></term>
    <listitem>
     <simpara>
-     RFC 3339 EXTENDED format
-     (example: <literal>2005-08-15T15:52:01.000+00:00</literal>)
+     RFC 3339 EXTENDED フォーマット
+     (例: <literal>2005-08-15T15:52:01.000+00:00</literal>)
     </simpara>
    </listitem>
   </varlistentry>
@@ -183,7 +184,7 @@
    <term><constant>DATE_RSS</constant></term>
    <listitem>
     <simpara>
-     RSS (example: <literal>Mon, 15 Aug 2005 15:52:01 +0000</literal>).
+     RSS (例: <literal>Mon, 15 Aug 2005 15:52:01 +0000</literal>).
      &Alias; <constant>DATE_RFC1123</constant>.
     </simpara>
    </listitem>
@@ -193,7 +194,7 @@
    <term><constant>DATE_W3C</constant></term>
    <listitem>
     <simpara>
-     World Wide Web Consortium (example: <literal>2005-08-15T15:52:01+00:00</literal>).
+     World Wide Web Consortium (例: <literal>2005-08-15T15:52:01+00:00</literal>).
      &Alias; <constant>DATE_RFC3339</constant>.
     </simpara>
    </listitem>