DESCRIPTION PROGRAMMABLE CONTROLLER Field [0001] The present invention relates to a programmable controller that controls an industrial controlled device. Background [0002] A programmable controller (hereinafter, PLC) controls a controlled device based on a user program and parameter files that define various parameters. These control files such as the user program and the parameter files are set by a programming device. Furthermore, not only the programming device but a programmable indicator or the like also refers to these control files. Conventionally, the PLC uses a fixed character-code set for communication with the programming device, the programmable indicator or the like (hereinafter, "external device"). [0003] A programmable indicator disclosed in Patent Literature 1 includes a plurality of sets of font data. Patent Literature 1 discloses a technique for switching the font data based on typeface identification information indicating a typeface of which country the characters are to be indicated. According to this technique, when an information process is performed using a common character-code set such as UNICODE, the characters can be indicated in an appropriate typeface even in a case where the typeface of the same code differs, by means of fonts of standard use depending on the countries to be used, for example. Citation List Patent Literature [0004] Patent Literature 1: Japanese Patent Application Laid-open No. 2000-227790 Summary Technical Problem [0005] However, the same character-code set is not always used for external devices connected to the PLC. It is assumed that a plurality of external devices using different character-code sets are connected to the PLC to which a usable character-code set is fixed to a specific code set. In this case, when the name of a file set by one of the external devices is to be read by another external device, so-called character corruption occurs in which the file name is not decoded into the same file name and another external device is disadvantageously unable to identify the file set to the PLC. [0006] The present invention has been achieved to solve the above problems, and an object of the present invention is to provide a programmable controller (PLC) capable of decoding the name of a file set to the PLC into the same name even if a plurality of external devices using mutually different character-code sets are connected to the PLC. Solution to Problem [0007] In order to solve the aforementioned problems, a programmable controller that controls an industrial controlled device according to one aspect of the present invention is configured to include: a storage unit that stores therein a control file for controlling the controlled device, to which a name described in character code relating to a first encoding method is assigned; a system unit that accesses the control file stored in the storage unit in response to a request from an external device; a character-code conversion table that associates character codes relating to a plurality of encoding methods including the first encoding method with one another for every character code decoded to the same character; and a character-code management unit which, in a case where an external device using a second encoding method different from the first encoding method is connected to the programmable controller and the character codes relating to the first encoding method are associated with character codes relating to the second encoding method one another in the character-code conversion table, converts an encoding method for a character code used to describe the name of a control file between the first encoding method and the second encoding method using the character-code conversion table at the time of transferring the name of the control file to be accessed between the external device and the system unit. Advantageous Effects of Invention [0008] As long as the character-code conversion table associates the character codes of an encoding method used by an external device with those relating to a first encoding method, the programmable controller according to the present invention can decode the name of a control file to the same name when an external device using different encoding method is connected to the PLC. Therefore, it is possible to decode the name of the file set to the PLC into the same name even if a plurality of external devices using mutually different character-code sets are connected to the PLC. Brief Description of Drawings [0009] FIG. 1 depicts a configuration of a PLC system configured to use a PLC according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of an example of a hardware configuration of a programming device. FIG. 3 is an explanatory diagram of an example of a hardware configuration of the PLC. FIG. 4 is an explanatory diagram of a functional configuration of a PLC system according to the embodiment of the present invention. FIG. 5 is an example of a data structure of a code page table. FIG. 6 is an explanatory diagram of an example of a data structure of a character-code conversion table. FIG. 7 is an explanatory diagram of a communication procedure for setting a character-code set performed by the PLC system. FIG. 8 is a flowchart for explaining operations performed by the PLC according to the embodiment of the present invention. FIG. 9 is a flowchart for explaining the operations performed by the PLC according to the embodiment of the present invention. Description of Embodiments [0010] Exemplary embodiments of a PLC according to the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments. [0011] Embodiment. FIG. 1 depicts a configuration of a PLC system configured to use a PLC according to an embodiment of the present invention. As shown in FIG. 1, a PLC system 1 is configured so that a PLC 2 is connected to a programming device 3. The connection between the PLC 2 and the programming device 3 is not limited to a specific method, but serial connection such as USB or Ethernet®, for example, is also applicable. The programming device that sets control files such as a user program and parameter files to the PLC 2 is described here as an example of an external device. However, the concept of the external device connected to the PLC 2 according to the present embodiment also embraces a programmable indicator that refers to a state of devices of the PLC 2 and to the control files set to the PLC 2. [0012] FIG. 2 is an explanatory diagram of an example of a hardware configuration of the programming device 3. The programming device 3 has a general computer configuration in which a CPU (Central Processing Unit) 31, a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a communication I/F 34, an input unit 35, and a display unit 36 are connected to one another by a bus. [0013] The display unit 36, which is a display device such as a liquid crystal display, displays output information such as an operation screen for a user based on an instruction from the CPU 31. The input unit 35 is configured to include a mouse and a keyboard, and an operation of the user for the programming device 3 is input to the input unit 35. The operation information input to the input unit 35 is transmitted to the CPU 31. The communication I/F 34 is a communication interface for the communication between the programming device 3 and the PLC 2. [0014] The RAM 33 is configured by a high-speed storage device such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory). The ROM 32 stores therein a PLC setting program 37 and a font dataset 38. The PLC setting program 37 is a computer program for setting the PLC 1. The font dataset 38 is an aggregate of image data (font data) for each character, and the image data for each character is associated with a code for each character included in a character-code set (a local character-code set A in the present embodiment) that defines a specific encoding method. Any character-code set is usable as the local character-code set A. As Japanese local character-code sets, ISO-2022-JP (JIS), Shift-JIS, EUC-JP and the like are widely used, and one of these can be used as the local character-code set. [0015] The PLC setting program 37 and the font dataset 38 are loaded into the RAM 33 by the CPU 31 via a bus line. The CPU 31 executes the PLC setting program 37 loaded into the RAM 33. At the time of setting the PLC 1 using the PLC setting program 37, the CPU 31 uses the encoding method defined by the local character-code set A. That is, characters that constitute the name of a control file (hereinafter, simply "files") to be output are encoded by using the encoding method defined by the local character-code set A. When displaying the name of the file on the display unit 36, the CPU 31 acquires font data corresponding to the codes of the respective characters that constitute the name of the file from the font dataset 38, and displays the name of the file on the display unit 36 using the thus acquired font data. For example, when the local character-code set A defines Shift-JIS and a character code "0x82A0" in Shift-JIS is described, the CPU 31 acquires font data for "